Old English gyrdan "put a belt or girdle around; encircle; bind with flexible material; invest with attributes," from Proto-Germanic *gurdjan (source also of Old Norse gyrða, Old Saxon gurdian, Old Frisian gerda, Dutch gorden, Old High German gurtan, German gürten), from PIE *ghr-dh-, suffixed form of root *gher- (1) "to grasp, enclose." Related: Girded; girding.
Throughout its whole history the English word is chiefly employed in rhetorical language, in many instances with more or less direct allusion to biblical passages. [OED]
As in to gird oneself "tighten the belt and tuck up loose garments to free the body in preparation for a task or journey."