ZILLAH (zĭl'a, Heb. tsillâh, shadow). One of the two wives of Cain’s descendant Lamech, the first known polygamist. She was the mother of Tubal-Cain, the patriarch of all workers in brass and iron (Gen.4.19-Gen.4.22).

ZILLAH zĭl’ ə (צִלָּֽה). One of Lamech’s wives, and the mother of Tubal-cain (Gen 4:19-23).

International Standard Bible Encyclopedia (1915)

One of Lamech’s wives (Ge 4:19,22,23). The name is perhaps connected with tsel, "shadow."