1. Belonging or peculiar to autumn; produced or gathered in autumn; belonging to the deeline of life.

2. A plant that flowers in autumn. The Autumnal equinox, the time when the sun crosses the equinox, about the 22nd of September.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• autuman,
• atumnal,
• autumnul,
• asturnal,
• zutumnal,
• sutumnal,
• wutumnal,
• qutumnal,
• aytumnal,
• ahtumnal,
• ajtumnal,
• aitumnal,
• a8tumnal,
• autimnal,
• autumal,
• auttumnal,
• cacumnal,
• Cutainal,
• Autuminal,
• Autamnal

The adjective form of the word "autumnal" is simply "autumnal" itself.

The plural form of "autumnal" is "autumnals".

The singular form of the word "autumnal" is "autumn"