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The Collaborative International Dictionary
Pentecosties

Pentecosty \Pen`te*cos"ty\, n.; pl. Pentecosties. [Gr. ?, fr. ? the fiftieth, ? fifty.] (Gr. Antiq.) A troop of fifty soldiers in the Spartan army; -- called also pentecostys.
--Jowett (Thucyd. ).

Wiktionary
pentecosties

n. (plural of pentecosty English)