Lewis Short
(adjective) : adverbiālis, e, adverbium
* Pertaining to an adverb, adverbial: super et subter adverbiales sunt, i. e. are sometimes used as adverbs, Charis. II. p. 182 P.: nomina,derived from adverbs,Prisc. IV. p. 619 P.: adjectivum, derived from an adverb, as externus from extra, id. II. p. 579.
Charlton T. Lewis, Charles Short, A Latin Dictionary