Liddell-Scott-Jones

πεντηκοστός (pentēkostos) fiftieth ^G:A

πεντηκοστός-ός, ή, όν,

fiftieth, [Refs 5th c.BC+]

__II substantive πεντηκοστόςή, ἡ,
__II.1 (i.e. μερίς), fiftieth part: hence, tax of two per century on exports and imports, at Athens, [πεντηκοστόςὰ τῶν λίθων “IG” 42(1).103.46 (Epid.); at Delos, [prev. work]22.1635.38 (4th c.BC), 11(2).161 A 26 (3rd c.BC) ">Refs 5th c.BC+]; at Halicarnassus, [Refs 3rd c.BC+]; τῶν πρηθέντων τελείτω π. [Refs 4th c.BC+]; = Latin quinquagesima, [πεντηκοστόςήν">Refs 2nd c.AD+] invented a new sort of composition of two per century in lieu of his cavalry service, i. e. paid this instead of it, [Refs 4th c.BC+]
__II.2 (i.e. ἡμέρα), fiftieth day (after the Passover), [LXX]; ἡ ἡμέρα τῆς Π. [NT]

_{LSJ Scripture Refs: Acts.2.1}