Lewis & Short

quīdam, quaedam, quoddam, and subst. quiddam, pron. indef., a certain, a certain one, somebody, something (v. aliquis init.): quidam ex advocatis, Cic. Clu. 63, 177: quidam de collegis nostris, id. Fam. 11, 21, 5: quaedam certa vox, id. de Or. 3, 12, 44: inopem quendam describere, id. Att. 7, 16: quodam tempore, a certain (indefinite) time, once upon a time, once, id. Fin. 5, 2, 4.
In plur., some: excesserunt urbe quidam, alii mortem sibi consciverunt, Liv. 45, 10: quaedam quaestiones, Cic. Top. 21, 79.
Also with gen.: quidam bonorum caesi, Tac. A. 1, 49: quibusdam Andriorum persuasit, etc., Liv. 31, 45, 7.
Often with an adj. to soften the assertion: timiditate quādam ingenuā, Cic. de Or. 2, 3, 10: qui virtutem duram et quasi ferream quandam esse volunt, id. Lael. 13, 48.
Subst.: quiddam, something; with gen.: quiddam mali, Cic. Leg. 3, 10, 23.
Without gen.: quiddam divinum, something divine, Cic. Ac. 1, 9, 33.
Plur.: quaedam, si credis consultis, mancipat usus, Hor. Ep. 2, 2, 159.