Charlton T. Lewis, An Elementary Latin Dictionary (aka. Elem. Lewis,) and

Charlton T. Lewis, Charles Short, A Latin Dictionary (aka. Lewis & Short)

dĕcennālis , e, adj. [decem-annus] ,

I. of ten years, decennial (late Lat.; cf. decennis): bellum, i. e. Caesar's in Gaul, Amm. 15, 12, 6 ; of the Trojan war, Hier. adv. Jovin. 1, 48 .--

II. Subst.: DECENNALIA (ium, n.), a festival celebrated every ten years after the time of Augustus, Trebell. Gallien. 21, 5; Inscr. Grut. 116, 4; v. decennis fin. (From Lewis & Short)