conspiracy
mid-14c., "a plotting of evil, unlawful design; a combination of persons for an evil purpose," from Anglo-French conspiracie, Old French conspiracie "conspiracy, plot," from Latin conspirationem (nominative conspiratio) "agreement, union, unanimity," noun of action from past-participle stem of conspirare "to agree, unite, plot," literally "to breathe together" (see conspire).
Earlier in same sense was conspiration (early 14c.), from French conspiration (13c.), from Latin conspirationem. An Old English word for it was facengecwis.
conspire + -acy
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." Or perhaps the notion is "to blow together" musical instruments, i.e., "to sound in unison."
Neutral or good sense of "to contribute jointly to a certain result" is from 1530s. Related: Conspired; conspiring.
con- + spirare
spirare (spirit)
「共に息をする」から、共謀する、謀るという意味に転じている
-acy
英語語源辞典によれば「語根 -aci- を含む形容詞あるいは-ateで終わる形容詞から抽象名詞を作る」または「-ateで終わる名詞から状態・職などを示す抽象名詞を造る」と書かれているが
conspire (v) はどちらにも該当しないように思われる？