dayjamas /deɪ̯ˈd͡ʒæ.məz/ noun[plural only]1 •Pajama-like clothing worn as daytime-appropriate apparel.DAYJAMAS FOR CASUAL AND LEISURE CLOTHING FOR MEN, WOMEN AND CHILDREN, NAMELY, SHIRTS, PANTS, SHORTS, SOCKS, SWEATERS AND JACKETS (U.S. CLS. 22 AND 39). — 1996