An adverbial clause is a clause that has an adverb -like function in modifying another clause.
An adverbial clause is likely to be distinct in its syntax or verb morphology.
(English)
He kept quiet in order to avoid trouble.
Thompson, Sandra A., and Robert E. Longacre. 1985. "Adverbial clauses." In Shopen 1985c
Pei, Mario A., and Frank Gaynor. 1954.A dictionary of linguistics. New York: Philosophical Library.
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Crystal, David. 1980.A first dictionary of linguistics and phonetics. Boulder, CO: Westview.