Lewis & Short

grātŭītus (grātŭĭtum, Stat. S. 1, 6, 16), a, um, adj. [gratia], that is done with, out pay, reward, or profit; free, spontaneous, voluntary, gratuitous (class.): ea (examina apium) vel aere parta vel gratuita contingunt, Col. 9, 8, 1: quid? liberalitas gratuitane est an mercenaria? si sine praemio benigna est, gratuita: si cum mercede, conducta, Cic. Leg. 1, 18, 48; cf.: probitas gratuita, id. Fin. 2, 31, 99: hominum caritas et amicitia gratuita est, id. N. D. 1, 44, 122: ne gratuita quidem suffragia, purchased, id. Planc. 22, 54; cf.: comitia gratuita, i. e. at which no gratuities were distributed to voters, id. Att. 4, 15, 8; id. Q. Fr. 2, 15, b, 4: pecunia, i. e. without interest, Plin. Ep. 3, 11, 2: cum debitor gratuita pecunia utatur, Paul. Sent. 2, 5, 1; so, usus pecuniae, Suet. Aug. 41: milies sestertio proposito, id. Tib. 48; and perh. also, fenus, lending without interest, id. Caes. 27: universi milites gratuitam et sine frumento stipendioque operam (obtulerunt), id. ib. 68: cadaverum et ruderum gratuita egestio, id. Ner. 38: gratuita in Circo loca, free places, id. Calig. 26: subsellia, free benches, id. Ner. 17: navis, a free ship or boat, Sen. Ben. 6, 19: furor, innate, spontaneous, Liv. 2, 42, 6: crudelitas, unprovoked, id. 3, 37, 8: praeterita parricidia, without effect, in vain, id. 1, 47, 1: AVGVSTALIS, without pay, Inscr. Orell. 3918; SO, SACERDOS, Inscr. ap. Maff. Mus. Ver. 80, 3: largis gratuitum cadit rapinis, Stat. S. 1, 6, 16: odium aut est ex offensa, aut gratuitum, unprovoked, Sen. Ep. 105, 3 (al. gratuito).
Hence, adv.: grātŭīto, without pay or profit, for naught, gratis, gratuitously: hic (Polygnotus) et Athenis porticum, quae Poecile vocatur, gratuito (pinxit), cum partem ejus Micon mercede pingeret, Plin. 35, 9, 35, § 59; Tac. A. 11, 22 fin.: neque tamen eloquentiam gratuito contingere, without cost, id. ib. 11, 7: multorum causas et non gravate et gratuito defendentis, Cic. Off. 2, 19, 66: cum mediocribus multis gratuito civitatem in Graecia homines impertiebant, for no particular reason, id. Arch. 5, 10; cf.: ne per otium torpescerent manus aut animus, gratuito potius malus atque crudelis erat, Sall. C. 16, 3 Kritz: gratuito nemo bonus est, id. H. 1, 48, 9.