conspire (v.) Look up conspire at Dictionary.com
late 14c., from Old French conspirer (14c.), from Latin conspirare "to agree, unite, plot," literally "to breathe together," from com "with, together" (see com-) + spirare "to breathe" (see spirit (n.)). Or perhaps the notion is "to blow together" musical instruments, i.e., "To sound in unison." Related: Conspired; conspiring.