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).

"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.

"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.

"to swindle," 1896, from con (adj.). Related: Conned; conning.

"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.

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.