warranty (n.)

c. 1200, "protector, defender," from Old North French warant "defender; surety, pledge; justifying evidence" (Old French garant), from Frankish *warand, from Proto-Germanic *war- "to warn, guard, protect" (source also of Old High German werento "guarantor," noun use of present participle of weren "to authorize, warrant;" German gewähren "to grant"), from PIE root *wer- (4) "to cover."

Sense evolved via notion of "permission from a superior which protects one from blame or responsibility" (early 14c.) to "document conveying authority" (1510s). A warrant officer in the military is one who holds office by warrant (as from a government department), rather than by commission (from a head of state).

because g- followed by some vowels in English usually has a "soft" pronunciation, a silent -u- sometimes was inserted between the g- and the vowel in Middle English to signal hardness, especially in words from French; but this was not done with many Scandinavian words where hard "g" precedes a vowel (gear, get, give, etc.). Germanic -w- generally became -gu- in words borrowed into Romance languages, but Old North French preserved the Frankish -w-, and English sometimes borrowed both forms, hence guarantee/warranty, guard/ward, etc.

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."