Is it ensure, insure, or assure?
"negation" (mainly in pro and con), 1570s, short for Latin contra "against" (see contra).
"study," early 15c., from Old English cunnan "to know, know how" (see can (v.1)).
a slang or colloquial shortening of various nouns beginning in con-, e.g., from the 19th century, confidant, conundrum, conformist, convict, contract, and from the 20th century, conductor, conservative.
"swindling," 1889, 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 ships," 1620s, from French conduire "to conduct, lead, guide" (10c.), from Latin conducere (see conduce). Related: Conned; conning.
"to swindle," 1896, from con (adj.). Related: Conned; conning.
Variant of com-.
A convict or former convict; prison inmate: You're a ''con,'' you've no rights (1893+)
[SF fandom] A science-fiction convention. Not used of other sorts of conventions, such as professional meetings. This term, unlike many others of SF-fan slang, is widely recognised even by hackers who aren't fans. "We'd been corresponding on the net for months, then we met face-to-face at a con."