Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
auctumnālis (correctly aut-), e (old form autumnal, related as facul to facile, volup to volupe, famul to famulus, Varr. ap. Charis. p. 94), adj. [auctumnus], of or pertaining to the autumn, autumnal: aequinoctium autumnal, Varr. ap. Charis. l. l.: aequinoctium autumnale, Varr. R. R. 1, 28 fin.; so Liv. 31, 47: (aestuus) tumentes autumnali (aequinoctio) amplius quam verno, Plin. 2, 97, 99, § 215: tempus autumnale, Varr. R. R. 1, 39, 1: lumen autumnale, * Cic. Arat. 285: agnus, Col. 7, 3, 11: rosa, Plin. 21, 4, 10, § 19: imbres, id. 19, 3, 13, § 37: pruna, Prop. 5, 2, 15: corna autumnalia, Ov. M. 8, 665, and 13, 816 et saep.