plier (n.)

"work with, practice with persistence, use or employ diligently," late 14c., shortened form of applien "join to, apply" (see apply). The core of this is Latin plicare "to lay, fold, twist," from Proto-Italic *plekt-, from PIE root *plek- "to plait." The sense of "travel regularly, go back and forth over the same course" is attested from 1803, perhaps from earlier sense "steer a course" (1550s). Related: Plied; plies; plying.