Extended Strong's Greek Lexicon (Abbott-Smith based)
autumnal
Usage: φθιν-οπωρινός, -ή, -όν (φθινόπωρον, late autumn), autumnal: δένδρα φ., autumn trees (said to be without fruit therefore at a time when fruit might be expected; see Mayor's elaborate note, Ep. Ju., 55-59, and reff. there): Ju 12.† (AS)