Easton's Bible Dictionary (1897)
Or Gashmu, firmness, probably chief of the Arabs south of Palestine, one of the enemies of the Jews after the return from Babylon (Neh. 2:19; 6:1, 2). He united with Sanballat and Tobiah in opposing the rebuilding of the wall of Jerusalem.
Smith's Bible Dictionary (1863)
and Gash’mu (rain), an Arabian, mentioned in (Nehemiah 2:19) and Nehe 6:1,2,6 (B.C. 446.) We may conclude that he was an inhabitant of Arabia Petraea or of the Arabian desert, and probably the chief of a tribe.” Gashum said it” made him a type of those who create a common report.
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
GE'SHEM (ram), also called GASH'MU, an Arabian who, with Sanballat and Tobiah, opposed Nehemiah while the wall was building. Neh 2:19; Neh 6:1-2.