Concise Bible Dictionary:

A Hebrew word, the definite meaning of which is not known. By the connection (“the Gammadims were in thy towers”) it appears to refer to the “guards,” as translated in the LXX (Ezek. 27:1111The men of Arvad with thine army were upon thy walls round about, and the Gammadims were in thy towers: they hanged their shields upon thy walls round about; they have made thy beauty perfect. (Ezekiel 27:11)). The margin of the RV has “valorous men.”