Origin and history of warrant

c. 1200, warant, "protector, defender, one who guards" (a sense now obsolete), 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"). In Watkins this is reconstructed to be from PIE root *wer- (4) "to cover."

It was extended by c. 1300 to "security or assurance provided via a protector; sanction; permission from a superior which protects one from blame or responsibility." Also by c.1300 in reference to letters, etc., serving as validation of authority.

It is attested by 1590s as "justifying reason or grounds for action, belief, etc." From early 14c. in law, "guarantee of a title or right to possession of property." 

Also from early 14c. as "power by official license," and by early 15c. as "written legal document authorizing or commanding some action; a writ." A military warrant officer is one who holds office by warrant (as from a government department), rather than by commission (from a head of state).

late 13c., waranten, "protect, defend against harm, keep safe from danger" (senses now obsolete), from Old North French warantir "safeguard, protect; guarantee, pledge" (Old French garantir), from warant (see warrant (n.)).

The meaning "to guarantee (goods for sale) to be of quality, give one's word for concerning" is attested from late 14c.; the sense of "to guarantee as true, assert as undoubted" is recorded from c. 1300. By c. 1400 in legal use, "to guarantee in possession." Related: Warranted; warranting.