-cy

suffix (see also -ACY, -ANCY, -CRACY, -ENCY, -MANCY).
1 denoting state or condition (bankruptcy; idiocy).
2 denoting rank or status (captaincy).
Etymology: from or after L -cia, -tia, Gk -k(e)ia, -t(e)ia

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-cy

suffix of ns., originating in L. -cia, -tia, Gr. -κια, -κεια, -τια, -τεια, in which the abstract ending -ia (-y) follows another formative element. Occurring chiefly in the combined forms -acy, -ancy, -ency, -cracy, -mancy, q.v. Also in prophecy, Gr. προϕητεία, f. προϕήτης prophet; policy, Gr. πολιτεία, f. πολίτης citizen, -polite, secrecy f. secret. In words in -acy from L. -ātia, and those in -ncy, the c represents an original t before i, which became c often in late L. and in French, e.g. L. infantia, late L. also infancia, F. enfance, infancy. Hence abstracts in -ncy arise out of adjs. or ns. in -nt, expressing the quality of an adjective (fluent, fluency), or the estate or position of an agent or officer (agent, agency). But by proximity of sound, -cy is extended from ns. in -nt to some in -n, e.g. chaplain-cy, captain-cy, alderman-cy (after incumbency, lieutenancy, adjutancy), and -cy being thus treated as an independent suffix = ship, is extended to other words as colonel-cy, and is even added to words in -t (instead of being substituted for the -t), as in bankrupt-cy (for which the regular etymological form is bankrupcy), idiot-cy variant of idiocy (Gr. ἰδιωτεία), baronet-cy, brevet-cy, cornet-cy (as against secret, secrecy).