Con
late 19th century (originally US): abbreviation of confidence, as in confidence trick .
wiktionary
From Middle English connen, from Old English cunnan(“to know, know how”), from Proto-Germanic *kunnaną, from Proto-Indo-European *ǵneh₃- (whence know). Doublet of can.
Abbreviation of Latin contra(“against”).
Clipping of convict.
From con trick, shortened from confidence trick.
From earlier cond; see conn.
Clipping of convention or conference.
Clipping of conversion.
Clipping of consumption.
etymonline
con (n.1, adv.)
"negation; in the negative; the arguments, arguers, or voters against a proposal" (mainly in pro and con), 1570s, short for Latin contra "against" (see contra (prep., adv.)). Compare pro (n.2).
con (adj.)
"swindling," 1889 (in con man), American English, from confidence man (1849), from the many scams in which the victim is induced to hand over money as a token of confidence. Confidence with a sense of "assurance based on insufficient grounds" dates from 1590s. Con artist is attested by 1910.
con (v.1)
"to guide a ship, give orders for the steering of a ship," 1620s, from French conduire "to conduct, lead, guide" (10c.), from Latin conducere "to lead or bring together, contribute, serve," from com "with, together" (see com-) + ducere "to lead" (from PIE root *deuk- "to lead"). As a noun, "action or post of steering a ship," 1825. Related: Conned; conning. Conning tower "dome-shaped pilot house of an ironclad warship or submarine" is attested from 1865.
con (v.2)
"to swindle," 1896, from con (adj.). Related: Conned; conning.
con (v.3)
"to study, get to know, peruse carefully," c. 1200, cunnen, "make an attempt, try or seek to do," from Old English cunnian "to know" (see can (v.1)). Related: Conned; conning.
con (n.2)
a slang or colloquial shortening of various nouns beginning in con-, such as, from the 19th century, confidant, conundrum, conformist, convict, contract, and from the 20th century, conductor, conservative.
