"preliminary examination or survey," specifically "an examination of a territory or enemy position with a view to directing military operations," 1810, a word from the Napoleonic Wars, from French reconnaissance "act of surveying," literally "recognition," from Old French reconoissance "recognition, acknowledgement" (see recognizance).
*gnō-, Proto-Indo-European root meaning "to know."
It forms all or part of: acknowledge; acquaint; agnostic; anagnorisis; astrognosy; can (v.1) "have power to, be able;" cognition; cognizance; con (n.2) "study;" connoisseur; could; couth; cunning; diagnosis; ennoble; gnome; (n.2) "short, pithy statement of general truth;" gnomic; gnomon; gnosis; gnostic; Gnostic; ignoble; ignorant; ignore; incognito; ken (n.1) "cognizance, intellectual view;" kenning; kith; know; knowledge; narrate; narration; nobility; noble; notice; notify; notion; notorious; physiognomy; prognosis; quaint; recognize; reconnaissance; reconnoiter; uncouth; Zend.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit jna- "know;" Avestan zainti- "knowledge," Old Persian xšnasatiy "he shall know;" Old Church Slavonic znati "recognizes," Russian znat "to know;" Latin gnoscere "get to know," nobilis "known, famous, noble;" Greek gignōskein "to know," gnōtos "known," gnōsis "knowledge, inquiry;" Old Irish gnath "known;" German kennen "to know," Gothic kannjan "to make known."
early 14c., reconisaunce, in law, "a bond acknowledging some obligation binding one over to do some particular act," from Old French reconissance "acknowledgment, recognition" (12c., Modern French reconnaissance), from reconoiss-, present-participle stem of reconoistre (see recognize).
By c. 1400 as "acknowledgment of subjection or allegiance" (to God or a temporal power). The general sense of "act of recognizing, acknowledgement of a person or thing" is from 15c. To be discharged or released (up)on (one's) own recognizance (1851) as a phrase for "be released without bail on condition of good behavior" in the jargon of police blotters and district courts, is based on the written promise that you sign to get it, to appear in court as required. Related: Recognizant.
1660s, "pod of the vanilla plant," from Spanish vainilla "vanilla plant," literally "little pod," diminutive of vaina "sheath," from Latin vagina "sheath of an ear of grain, hull of a plant" (see vagina). So called from the shape of the pods. European discovery 1521 by Hernando Cortes' soldiers on reconnaissance in southeastern Mexico. Meaning "flavoring extracted from the vanilla bean" is attested by 1728.
Adjectival meaning "conventional, of ordinary sexual preferences" is by 1970s, probably from the notion of whiteness and the common choice of vanilla ice cream; vanilla as figurative of a plain and conventional choice (without reference to sex) seems to date to the late 19c. as a noun, by 1940s (often plain vanilla) as an adjective.