piracy n.

c. 1300 (mid-13c. as a surname), "a sea-robber, sea-plunderer, one who without authority and by violence seizes or interferes with the ship or property of another on the sea," especially one who is habitually engaged in such robbery or sails the seas for the robbery and plunder of merchant vessels, from Old French pirate and directly from Medieval Latin pirata "sailor, corsair, sea robber" (source also of Spanish, Italian pirata, Dutch piraat, German Pirat), from classical Latin, from Greek peiratēs "brigand, pirate," literally "one who attacks" (ships), from peiran "to attack, make a hostile attempt on, try," from peira "trial, an attempt, attack" (from PIE *per-ya-, suffixed form of root *per- (3) "to try, risk").

An Old English word for it was sæsceaða ("sea-scather"); a pirate-ship was a ðeofscip ("thief-ship"). Figurative sense of "plunderer, despoiler" is from late 15c. Meaning "one who takes another's work without permission" first recorded 1701; sense of "unlicensed radio broadcaster" (generally transmitting from a ship outside territorial waters)  is from 1913.

word-forming element making nouns of quality, state, or condition, a confusion in English of three similar suffixes from Latin:

1. in primacy, etc., from Old French -acie and directly from Medieval Latin -acia, Late Latin -atia, making nouns of quality, state, or condition from nouns in -as.

2. in advocacy, etc., from Late Latin -atia, forming nouns of state from nouns in -atus.

3. in fallacy, etc., from Latin -acia, forming nouns of quality from adjectives in -ax (genitive -acis). Also forming part of -cracy. It has been extended in English to nouns not found in Latin (accuracy) and to non-Latin words (piracy).