1. Conspire definition, to agree together, especially secretly, to do something wrong, evil, or illegal: They Conspired to kill the king

2. Late 14c., "aspire or plan maliciously, agree together to commit a criminal or reprehensible act," from Old French Conspirer (14c.), from Latin conspirare "to agree, unite, plot," literally "to breathe together," from assimilated form of com "with, together" (see con-) + spirare "to breathe" (see spirit (n.)), perhaps on the notion of "to agree (by spoken oath) to commit a bad act."

3. Late 14c., "aspire or plan maliciously, agree together to commit a criminal or reprehensible act," from Old French Conspirer (14c.), from Latin conspirare "to agree, unite, plot," literally "to breathe together," from assimilated form of com "with, together" (see con-) + spirare "to breathe" (see spirit (n.)), perhaps on the notion of "to agree (by spoken oath) to commit a bad act."