Online Etymology Dictionary

imperforate (adj.): 1670s, from im- + perforate (adj.).
imperial (adj.): late 14c., "having a commanding quality," from Old French imperial (12c.), from Latin imperialis "of the empire or emperor," from imperium (see empire). Meaning "pertaining to an empire" (especially the Roman) is from late 14c. Imperial presidency in a U.S. context traces to Arthur Schlesinger Jr.'s book on the Nixon administration (1974). Related: Imperially.
imperialism (n.): 1826, "advocacy of empire," originally in a Napoleonic context, also of Rome and of British foreign policy, from imperial + -ism. At times in British usage (and briefly in U.S.) with a neutral or positive sense relating to national interests or the spread of the benefits of Western civilization, but from the begining usually more or less a term of reproach. General sense of "one country's rule over another," first recorded 1878. Picked up disparagingly in Communist jargon by 1918.
It is the old story of 1798, when French republicanism sick of its own folly and misdeeds, became metamorphosed into imperialism, and consoled itself for its incapacity to found domestic freedom by putting an iron yoke upon Europe, and covering it with blood and battle-fields. [Francis Lloyd, "St. James's Magazine," January 1842]
imperialist (n.): c.1600, "an adherent of an emperor," such as the emperor of Germany, France, China, etc., probably modeled on French impérialiste (early 16c.); from imperial + -ist. The shift in meaning to "advocate of imperialism" (1893) came via the British Empire, which involved a worldwide colonial system. See imperialism. As a term of abuse in communist circles, attested by 1918. As an adjective by 1816.
imperialistic (adj.): 1872, from imperial + -istic. Also see imperialist.
imperil (v.): 1590s, from assimilated form of in- "into, in" (see in- (2)) + peril. Related: Imperiled; imperiling.
imperious (adj.): 1540s, from Latin imperiosus "commanding, mighty, powerful," from imperium "empire, command" (see empire). Related: Imperiously.
imperishable (adj.): 1640s, from assimilated form of in- "not, opposite of" (see in- (1)) + perishable.
imperium (n.): 1650s, from Latin imperium "command, supreme authority, power" (see empire).
impermanence (n.): 1796, from impermanent + -ence. Impermanency is from 1640s.
impermanent (adj.): 1650s, from assimilated form of in- "not, opposite of" (see in- (1)) + permanent.
impermeable (adj.): 1690s, from French imperméable, from Late Latin impermeabilis, from assimilated form of in- "not, opposite of" (see in- (1)) + permeabilis (see permeable).
impermissible (adj.): 1814, from assimilated form of in- "not, opposite of" (see in- (1)) + permissible.
imperscriptable (adj.): "unrecorded, without written authority," 1832, used only with right. From assimilated form of Latin in- "not, opposite of" (see in- (1)) + perscribere "to write down."
impersonal (adj.): mid-15c., a grammatical term, from Late Latin impersonalis, from assimilated form of in- "not, opposite of" (see in- (1)) + personalis "personal" (see personal). Sense of "not connected with any person" is from 1620s; that of "not endowed with personality" is from 1842. Related: impersonally.
impersonality (n.): 1769, from impersonal + -ity.
impersonate (v.): 1620s, "to invest with a personality," from assimilated form of Latin in- "into, in" (see in- (2)) + persona "person." Sense of "to assume the person or character of" is first recorded 1715. Earlier in same sense was personate (1610s). Related: Impersonated; impersonating.
impersonation (n.): 1800, "personification;" 1825 as "an acting of a part or character;" noun of action from impersonate (v.).
impersonator (n.): "one who assumes the person or character of another," 1853, from impersonate with Latinate agent noun suffix.
impertinence (n.): c.1600, from French impertinence, from Medieval Latin impertinentia, from Late Latin impertinentem "not belonging" (see impertinent). Impertinency is from 1580s.
impertinent (adj.): late 14c., "unconnected, unrelated, not to the point," from Old French impertinent (14c.) or directly from Late Latin impertinentem (nominative impertinens) "not belonging," literally "not to the point," from assimilated form of Latin in- "not, opposite of" (see in- (1)) + pertinens (see pertinent). Sense of "rudely bold" is 1680s, from earlier sense of "not appropriate to the situation," probably modeled on similar use in French, especially by Molière, from notion of meddling with what is beyond one's proper sphere.
impertinently (adv.): mid-15c., from impertinent + -ly (2).
imperturbable (adj.): c.1500, from Middle French imperturbable and directly from Late Latin imperturbabilis "that cannot be disturbed" (Augustine), from assimilated form of in- "not, opposite of" (see in- (1)) + *perturbabilis, from Latin perturbare "to confuse, disturb" (see perturb). Related: Imperturbably; imperturbability.
impervious (adj.): 1640s, from Latin impervius "that cannot be passed through," from assimilated form of in- "not, opposite of" (see in- (1)) + pervius "letting things through," from per "through" + via "road." Related: Imperviously; imperviousness.
impetigo (n.): pustular disease of the skin, late 14c., from Latin impetigo "skin eruption," from impetere "to attackâ" (see impetus). Related: Impetiginous.
impetuosity (n.): early 15c., "violent movement, rushing," from Old French impetuosité (13c.), from Medieval Latin impetuositatem (nominative impetuositas), from Late Latin impetuosus (see impetuous).
impetuous (adj.): late 14c., "hot-tempered, fierce," from Old French impetuos (13c.) and directly from Late Latin impetuosus "impetuous, violent," from Latin impetus "attack" (see impetus). Related: Impetuously; impetuousness.
impetus (n.): early 15c., impetous "rapid movement, rush;" 1640s, with modern spelling, "force with which a body moves, driving force," from Latin impetus "attack, assault, onset, impulse, violence, vigor, force, passion," related to impetere "to attack," from assimilated form of in- "into, in, on, upon" (see in- (2)) + petere "aim for, rush at" (see petition (n.)).
impiety (n.): mid-14c., from Old French impieté (12c.), from Latin impietatem (nominative impietas) "irreverence, ungodliness; disloyalty, treason," noun of quality from impius (see impious).
impinge (v.): 1530s, "fasten or fix forcibly," from Latin impingere "drive into, strike against," from assimilated form of in- "into, in, on, upon" (see in- (2)) + pangere "to fix, fasten" (see pact). Sense of "encroach, infringe" first recorded 1738. Related: Impinged; impinging.
impingement (n.): 1670s; see impinge + -ment.
impious (adj.): 1590s, from Latin impius "without reverence, irreverent, wicked; undutiful, unpatriotic," from assimilated form of in- "not, opposite of" (see in- (1)) + pius (see pious). Related: Impiously; impiousness.
impish (adj.): 1650s, from imp + -ish. Related: Impishly; impishness.
implacability (n.): 1530s, from Late Latin implacabilitas, from Latin implacabilis (see implacable).
implacable (adj.): early 15c., from Old French implacable, from Latin implacabilis "unappeasable," from assimilated form of in- "not, opposite of" (see in- (1)) + placabilis "easily appeased" (see placate). Related: Implacably.
implant (v.): early 15c., from French implanter "to insert, engraft," from assimilated form of in- "into, in, on, upon" (see in- (2)) + planter "to plant" (see plant (n.)). Related: Implanted; implanting.
implant (n.): 1890 as "thing implanted;" 1941 as "action of implanting," from implant (v.). Related: Implants, by 1981 as short for breast implants (1976).
implantation (n.): 1570s, from French implantation, noun of action from implanter (see implant (v.)).
implausibility (n.): 1630s; see implausible + -ity.
implausible (adj.): c.1600, from assimilated form of in- "not, opposite of" (see in- (1)) + plausible. Related: Implausibly.
implement (n.): mid-15c., from Late Latin implementem "a filling up" (as with provisions), from Latin implere "to fill," from assimilated form of in- "into, in, on, upon" (see in- (2)) + plere "to fill" (see pleio-). Sense of "tool" is 1530s, from notion of things provided to do work, that which "fills up" or "completes" a household (c.1500).
implement (v.): 1806, originally chiefly in Scottish, where the noun was a legal term meaning "fulfillment," from from implement (n.). It led to the wretched formation implementation, first recorded 1913. Related: Implemented.
implicate (v.): early 15c., "to convey in a fable;" c.1600, "intertwine, wreathe," from Latin implicatus, past participle of implicare "to involve, entwine" (see implication). Meaning "involve a person in a crime, charge, etc.," is from 1797. Related: Implicated; implicating.
implication (n.): early 15c., "action of entangling," from Latin implicationem (nominative implicatio) "interweaving, entanglement," from past participle stem of implicare "involve, entangle, connect closely," from assimilated form of in- "into, in, on, upon" (see in- (2)) + plicare "to fold" (see ply (v.1)). Meaning "something implied (but not expressed)" is from 1550s.
implications (n.): see implication.
implicit: 1590s, from Middle French implicite and directly from Latin implicitus, later variant of implicatus, past participle of implicare (see implication).
implicitly (adv.): c.1600, from implicit + -ly (2).
implode (v.): 1870 (implied in imploded), back-formation from implosion. Related: Imploding.
implore (v.): c.1500, from Middle French implorer and directly from Latin implorare "call for help, beseech," originally "invoke with weeping," from assimilated form of in- "on, upon" (see in- (2)) + plorare "to weep, cry out." Related: Implored; imploring; imploringly.
implosion (n.): "a bursting inward," 1829, modeled on explosion, with assimilated form of in- "into, in, on, upon" (see in- (2)).
And to show how entire the neglect and confusion have been, they speak in the same breath of all these explosions, and of the explosion of a mixture of hydrogen and oxygen, the result of which, instead of being a gas or an enlargement of bulk, a positive quantity, is a negative one. It is a vacuum, in a popular sense, because the produce is water. The result is an implosion (to coin a word), not an explosion .... ["Gas-light," "Westminster Review," October 1829]
In early use often in reference to effect of deep sea pressures, or in phonetics. Figurative sense is by 1960.