Etymology
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warn (v.)

Old English warnian "to give notice of impending danger," also intransitive, "to take heed," from Proto-Germanic *warōnan (source also of Old Norse varna "to admonish," Old High German warnon "to take heed," German warnen "to warn"), from PIE root *wer- (4) "to cover." Related: Warned; warning.

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forewarn (v.)
early 14c., from fore- + warn. Related: Forewarned; forewarning.
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warning (n.)
"notice beforehand of the consequences that will probably follow continuance in some particular course" [Century Dictionary], Old English warnung, verbal noun from warnian (see warn (v.)).
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garnish (v.)

late 14c., "to decorate, adorn, beautify," also in Middle English "equip (a place) for defense; arm (oneself) for battle; prepare to defend," from Old French garniss-, present participle stem of garnir "provide, furnish; fortify, reinforce" (11c.), from Frankish *warnjan, from Proto-Germanic *warnon "be cautious, guard, provide for" (source also of Old High German warnon "to take heed," Old English warnian "to take warning, beware;" see warn), from PIE root *wer- (4) "to cover."

Sense evolution is from "arm oneself" to "fit out" to "embellish," which was the earliest meaning in English. Culinary sense of "to decorate a dish for the table" predominated after c. 1700. Older meaning survives in legal sense of "to warn or serve notice of attachment of funds" (1570s). Related: Garnished; garnishing.

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*wer- (4)

Proto-Indo-European root meaning "to cover."

It forms all or part of: aperitif; apertive; aperture; barbican; cover; covert; curfew; discover; garage; garment; garnish; garret; garrison; guarantee; guaranty; kerchief; landwehr; operculum; overt; overture; pert; warn; warrant; warrantee; warranty; warren; wat; Wehrmacht; weir.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vatah "enclosure," vrnoti "covers, wraps, shuts;" Lithuanian užveriu, užverti "to shut, to close;" Old Persian *pari-varaka "protective;" Latin (op)erire "to cover," (ap)erire "open, uncover" (with ap- "off, away"); Old Church Slavonic vora "sealed, closed," vreti "shut;" Old Irish feronn "field," properly "enclosed land;" Old English wer "dam, fence, enclosure," German Wehr "defense, protection," Gothic warjan "to defend, protect."

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admonish (v.)

mid-14c., amonesten "remind, urge, exhort, warn, give warning," from Old French amonester "urge, encourage, warn" (12c.), from Vulgar Latin *admonestare, from Latin admonere "bring to mind, remind (of a debt);" also "warn, advise, urge," from ad "to," here probably with frequentative force (see ad-) + monere "to admonish, warn, advise," from PIE *moneie- "to make think of, remind," suffixed (causative) form of root *men- (1) "to think."

The -d- was restored on Latin model in English as in French (Modern French admonester). The ending was influenced by words in -ish (such as astonish, abolish). Related: Admonished; admonishing. Latin also had commonere "to remind," promonere "to warn openly," submonere "to advise privately" (source of summon).

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caution (v.)

"to warn, exhort to take heed," 1640s, from caution (n.). Related: Cautioned; cautioning.

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lighthouse (n.)
tower exhibiting lights to warn mariners of rocks, shoals, etc., 1620s, from light (n.) + house (n.).
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admonitory (adj.)
"containing an admonition," 1590s, from Late Latin admonitorius, from Latin admonitus, past participle of admonere "to advise; to warn" (see admonish). Related: Admonitorily; admonitorial.
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premonitory (adj.)

"serving to warn or notify beforehand," 1640s, from Late Latin praemonitorius, from praemonitor, agent noun from stem of praemonere "forewarn" (see premonition).

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