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The Collaborative International Dictionary
Pentecoster

Pentecoster \Pen`te*cos"ter\, n. [NL., fr. Gr. ?, fr. ? fifty.] (Gr. Antiq.) An officer in the Spartan army commanding fifty men.
--Mitford.

Wiktionary
pentecoster

n. (context historical Ancient Greece English) An officer in the Spartan army commanding fifty men.