Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
lēgālis, e, adj. [lex], of or belonging to the law, legal (post-Aug.): genus quaestionis, Quint. 3, 5, 4; cf. id. 3, 6, 86 sq.: quaestiones, id. 3, 6, 46: status, id. 3, 6, 45: tractatus, id. 3, 8, 4: vita, according to the (divine) law, pious, Tert. adv. Marc. 4, 25.
Hence, adv.: lēgālĭter, according to law, legally: adversarium provocare legaliter, Cassiod. Ep. 4, 37: de homicidiis Moyses legaliter dicit, i. e. in laying down the law, Mos. et Rom. Leg. Coll. 1, 5 prooem.