Etymology
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impervious (adj.)
1640s, from Latin impervius "not to be traverse, that cannot be passed through, impassible," from assimilated form of in- "not, opposite of" (see in- (1)) + pervius "letting things through, that can be passed through," from per "through" (from PIE root *per- (1) "forward," hence "through") + via "road" (see via (adv.)). Related: Imperviously; imperviousness.
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*wegh- 

Proto-Indo-European root meaning "to go, move, transport in a vehicle."

The root wegh-, "to convey, especially by wheeled vehicle," is found in virtually every branch of Indo-European, including now Anatolian. The root, as well as other widely represented roots such as aks- and nobh-, attests to the presence of the wheel — and vehicles using it — at the time Proto-Indo-European was spoken. [Watkins, p. 96]

It forms all or part of: always; away; convection; convey; convex; convoy; deviate; devious; envoy; evection; earwig; foy; graywacke; impervious; invective; inveigh; invoice; Norway; obviate; obvious; ochlocracy; ogee; pervious; previous; provection; quadrivium; thalweg; trivia; trivial; trivium; vector; vehemence; vehement; vehicle; vex; via; viaduct; viatic; viaticum; vogue; voyage; wacke; wag; waggish; wagon; wain; wall-eyed; wave (n.); way; wee; weigh; weight; wey; wiggle.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vahati "carries, conveys," vahitram, vahanam "vessel, ship;" Avestan vazaiti "he leads, draws;" Greek okhos "carriage, chariot;" Latin vehere "to carry, convey," vehiculum "carriage, chariot;" Old Church Slavonic vesti "to carry, convey," vozŭ "carriage, chariot;" Russian povozka "small sled;" Lithuanian vežu, vežti "to carry, convey," važis "a small sled;" Old Irish fecht "campaign, journey," fen "carriage, cart;" Welsh gwain "carriage, cart;" Old English wegan "to carry;" Old Norse vegr, Old High German weg "way;" Middle Dutch wagen "wagon."

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*per- (1)

Proto-Indo-European root forming prepositions, etc., meaning "forward," and, by extension, "in front of, before, first, chief, toward, near, against," etc.

It forms all or part of: afford; approach; appropriate; approve; approximate; barbican; before; deprive; expropriate; far; first; for; for-; fore; fore-; forefather; foremost; former (adj.); forth; frame; frau; fret; Freya; fro; froward; from; furnish; furniture; further; galore; hysteron-proteron; impervious; improbity; impromptu; improve; palfrey; par (prep.); para- (1) "alongside, beyond; altered; contrary; irregular, abnormal;" paradise; pardon; paramount; paramour; parvenu; pellucid; per; per-; percent; percussion; perennial; perestroika; perfect; perfidy; perform; perfume; perfunctory; perhaps; peri-; perish; perjury; permanent; permeate; permit; pernicious; perpendicular; perpetual; perplex; persecute; persevere; perspective; perspire; persuasion; pertain; peruse; pervade; pervert; pierce; portray; postprandial; prae-; Prakrit; pre-; premier; presbyter; Presbyterian; preterite; pride; priest; primal; primary; primate; primavera; prime; primeval; primitive; primo; primogenitor; primogeniture; primordial; primus; prince; principal; principle; prior; pristine; private; privilege; privy; pro (n.2) "a consideration or argument in favor;" pro-; probably; probe; probity; problem; proceed; proclaim; prodigal; produce; profane; profess; profile; profit; profound; profuse; project; promise; prompt; prone; proof; proper; property; propinquity; prophet; prose; prostate; prosthesis; protagonist; Protean; protect; protein; Proterozoic; protest; proto-; protocol; proton; protoplasm; Protozoa; proud; prove; proverb; provide; provoke; prow; prowess; proximate; Purana; purchase; purdah; reciprocal; rapprochement; reproach; reprove; veneer.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit pari "around, about, through," parah "farther, remote, ulterior," pura "formerly, before," pra- "before, forward, forth;" Avestan pairi- "around," paro "before;" Hittite para "outside of," Greek peri "around, about, near, beyond," pera "across, beyond," paros "before," para "from beside, beyond," pro "before;" Latin pro "before, for, on behalf of, instead of," porro "forward," prae "before," per "through;" Old Church Slavonic pra-dedu "great-grandfather;" Russian pere- "through;" Lithuanian per "through;" Old Irish ire "farther," roar "enough;" Gothic faura "before," Old English fore (prep.) "before, in front of," (adv.) "before, previously," fram "forward, from," feor "to a great distance, long ago;" German vor "before, in front of;" Old Irish air- Gothic fair-, German ver-, Old English fer-, intensive prefixes.

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athermanous (adj.)
"heat-resistant, impervious to radiant heat," 1839, from a- (3) "not, without" + Greek thermainein "impart heat," from thermos "hot" (see thermal).
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opacity (n.)

1550s, "darkness of meaning, obscurity," from French opacité, from Latin opacitatem (nominative opacitas) "shade, shadiness," from opacus "shaded, dark, opaque," a word of unknown origin. The literal sense "condition of being impervious to light; quality of a body which renders it impervious to rays of light" in English is recorded from 1630s.

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opaque (adj.)

early 15c., opake, "dark, shaded, unlit" (a sense now obsolete), from Latin opacus "shaded, in the shade, shady, dark, darkened, obscure," of unknown origin. Spelling influenced after c. 1650 by French opaque (c. 1500), from the Latin. Meaning "impervious to the rays of light" is from 1640s. Figurative sense of "obscure, hard to understand" is from 1761. Related: Opaquely; opaqueness.

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repellent (adj.)

also repellant, "having the effect of repelling," 1640s, from Latin repellentem (nominative repelens), present participle of repellere (see repel). Originally of medicines that reduce tumors; the meaning "morally repelling, repulsive, distasteful, disagreeable" is recorded by 1797.

That is repellent which keeps one at arm's length ; that is repulsive from which one recoils ; that is, the second is a much stronger word. [Fowler, 1926]

By 1805 in the specific sense of "capable of repelling water, impervious to moisture." 

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staunch (adj.)
early 15c., "impervious to water," from Old French estanche "firm, watertight," fem. of estanc "tired, exhausted, wearied, vanquished; water-tight; withered, dried" (Modern French étanche), from Vulgar Latin *stanticare (source also of Spanish estanco "water-tight," Italian stanco "exhausted, weary"), probably from Latin stans (genitive stantis), present participle of stare "to stand," from PIE root *sta- "to stand, make or be firm." Sense of "strong, substantial" first recorded mid-15c.; of persons, "standing firm and true to one's principles" from 1620s.
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Everglades (n.)

1826, from everglade (1823), from ever, apparently in sense of "endless" + glade. Charles Vignoles's "Observations upon the Floridas" (1823) has Eternal Glades and Ever Glade morass.

The distance from the mouth of Hilsborough river to the head of the lake, in a direct line, is about 110 statute miles. The country between them is mostly, if not wholly, an everglade, by which is meant a low marsh frequently covered with water, and in which there grows a sharp triangular grass, from ten to twelve feet high, and impervious to men or animals. [American Mechanics' Magazine, Jan. 21, 1826]
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