Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
lūsĭo, ōnis, f. [ludo], a playing, play: in ludum discendi, non lusionis, Cic. Q. Fr. 3, 4, 6: pueri lusionibus vel laboriosis delectantur, id. Fin. 5, 20, 55: in ipsā lusione (pilae), in the act of playing, id. de Or. 1, 16, 73: pilaris lusio, Stat. S. 4 praef.