Old English tæcan (past tense tæhte, past participle tæht) "to show, point out, declare, demonstrate," also "to give instruction, train, assign, direct; warn; persuade," from Proto-Germanic *taikijan "to show" (source also of Old High German zihan, German zeihen "to accuse," Gothic ga-teihan "to announce"), from PIE root *deik- "to show, point out." Related to Old English tacen, tacn "sign, mark" (see token). Related: Taught; teaching.

Lemonade Vendor (Edgar Kennedy), enraged: I'll teach you to kick me!

Chico: you don't have to teach me, I know how. [kicks him]

The usual sense of Old English tæcan was "show, declare, warn, persuade" (compare German zeigen "to show," from the same root); while the Old English word for "to teach, instruct, guide" was more commonly læran, source of modern learn and lore.

early 14c., "announce, make known in a formal manner" (a sense now obsolete), from Old French denoncier (12c., Modern French dénoncer) and directly from Latin denuntiare "to announce, proclaim; denounce, menace; command, order," from de- "down" + nuntiare "proclaim, announce," from nuntius "messenger" (from PIE root *neu- "to shout").

The negative sense in English developed (probably encouraged by other words in de-) via the meanings "proclaim as cursed, excommunicated, removed from office" (early 14c.); "formally or publicly threaten to do" (1630s); "declare or proclaim to be cursed, wicked, or evil" (1660s). The meaning "make formal or public accusation against, inform against, accuse" (especially in turning on one's co-conspirators) is from late 15c. Related: Denounced; denouncing.

c. 1300, "to make reasoned statements to prove or refute a proposition," from Old French arguer "maintain an opinion or view; harry, reproach, accuse, blame" (12c.), ultimately from Latin arguere "make clear, make known, prove, declare, demonstrate" (from  a suffixed form of PIE root *arg- "to shine; white"). The transmission to French might be via arguere in a Medieval Latin sense of "to argue," or from Latin argutare "to prattle, prate," frequentative of arguere.

De Vaan says arguere is probably "a denominative verb 'to make bright, enlighten' to an adj. *argu- 'bright' as continued in argutus and outside Italic." He cites a closely similar formation in Hittite arkuuae- "to make a plea." The meaning "to oppose, dispute, contend in argument" is from late 14c. Related: Argued; arguing.

late 13c., sclaundren, "defame, caluminate, accuse falsely and maliciously," from Anglo-French esclaundrer, Old French esclandrer, from Old French esclandre "scandalous statement" (see slander (n.)). Related: Slandered; slandering; slanderer. In early biblical translations also sometimes closer to the Latin literal sense, or with a notion of "stumbling block to faith, grace, etc."

And who euer schal sclaundre oon of these litle that bileuen in me, it were betere to hym that a mylne stoon of assis were don aboute his necke, and he were cast in to the see. [Mark ix.42]

Where KJV has "And whosoever shall offend one of these little ones that believe in me, it is better for him that a millstone were hanged about his neck, and he were cast into the sea."

Proto-Indo-European root meaning "to show," also "pronounce solemnly," "also in derivatives referring to the directing of words or objects" [Watkins].

It forms all or part of: abdicate; abdication; addict; adjudge; apodictic; avenge; benediction; betoken; condition; contradict; contradiction; dedicate; deictic; deixis; dictate; diction; dictionary; dictum; digit; disk; ditto; ditty; edict; Eurydice; index; indicate; indication; indict; indiction; indictive; indite; interdict; judge; judicial; juridical; jurisdiction; malediction; malison; paradigm; policy (n.2) "written insurance agreement;" preach; predicament; predicate; predict; prejudice; revenge; soi-disant; syndic; teach; tetchy; theodicy; toe; token; valediction; vendetta; verdict; veridical; vindicate; vindication; voir dire.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dic- "point out, show;" Greek deiknynai "to show, to prove," dike "custom, usage;" Latin dicere "speak, tell, say," digitus "finger," Old High German zeigon, German zeigen "to show," Old English teon "to accuse," tæcan "to teach."

c. 1300, "to fall (into water) or strike with a full impact," a common Low German word, from or related to Middle Dutch and Dutch plompen, East Frisian plumpen, Middle Low German plumpen, probably more or less imitative of something hard striking something soft. Perhaps influenced by or merged with Middle English plumben "immerse (in liquid)," late 14c., from plumb (n.) in the "weight" sense. Hence plump (n.) "a firm blow," in pugilism usually one to the belly.

To plump; to strike, or shoot. I'll give you a plump in the bread basket, or the victualling office; I'll give you a blow in the stomach. [Grose, "Dictionary of the Vulgar Tongue," London, 1785]

Or, even if any of them should suspect me, I know how to bring myself off. It is but pretending to be affronted, stripping directly, challenging him to fight, and before he can be on his guard, hitting him a plump in the bread-basket, that shall make him throw up his accounts; and I'll engage he will have but very little stomach to accuse me after. ["The Reverie: or A Flight to the Paradise of Fools," London, 1763]

As an adverb, "at once," as in a sudden fall, from 1590s.

element meaning "into, in, on, upon" (also im-, il-, ir- by assimilation of -n- with following consonant), from Latin in- "in," from PIE root *en "in."

In Old French (and hence in Middle English) this often became en-, which in English had a strong tendency to revert to Latin in-, but not always, which accounts for pairs such as enquire/inquire. There was a native form, which in West Saxon usually appeared as on- (as in Old English onliehtan "to enlighten"), and some of those verbs survived into Middle English (such as inwrite "to inscribe"), but all now seem to be extinct.

Not related to in- (1) "not," which also was a common prefix in Latin, causing confusion: to the Romans impressus could mean "pressed" or "unpressed;" inaudire meant "to hear," but inauditus meant "unheard of;" in Late Latin investigabilis could mean "that may be searched into" or "that cannot be searched into." Latin invocatus was "uncalled, uninvited," but invocare was "to call, appeal to."

The trouble has continued in English; the hesitation over what is meant by inflammable being a commonly cited example. Implume (1610s) meant "to feather," but implumed (c. 1600) meant "unfeathered." Impliable can mean "capable of being implied" (1865) or "inflexible" (1734). Impartible in 17c. could mean "incapable of being divided" or "capable of being imparted." Impassionate can be "free from passion" or it can mean "strongly stirred by passion." Inanimate (adj.) is "lifeless," but Donne uses inanimate (v.) to mean "infuse with life or vigor." Irruption is "a breaking in," but irruptible is "unbreakable."

In addition to improve "use to one's profit," Middle English also had a verb improve meaning "to disprove" (15c.). To inculpate is "to accuse," but inculpable means "not culpable, free from blame." Infestive has meant "troublesome, annoying" (1560s, from infest) and "not festive" (1620s). In Middle English inflexible could mean "incapable of being bent" or "capable of being swayed or moved." In 17c., informed could mean "current in information," formed, animated," or "unformed, formless" ("This was an awkward use" [OED]). Inhabited has meant "dwelt in" (1560s) and "uninhabited" (1610s); inhabitable likewise has been used on opposite senses, a confusion that goes back to Late Latin.