An English habitational surname from Old English [æt þǣre] sīdan īeġe (“[at the] wide island”). / A male or female given name transferred from the surname.

(Cambridge University, informal) Ellipsis of Sidney Sussex College, Cambridge..

(UK, humorous) steak and kidney pie

(biology, game theory) A model for the evolution and maintenance of informative communication between relatives, developed to explain begging behaviour in chicks.

plural of Sir Philip Sidney game

Of or relating to Sir Philip Sidney (1554–1586), English poet and scholar.