What is "presby-"

word-forming element meaning "old," from Greek presby-, combining form of presbys "elder, old man," possibly originally "one who leads the cattle," from *pres- "before," extended form of *pre- (see per) + root of bous "cow." Watkins, however, has it from PIE *pres-gwu- "going before," with second element from root *gw-u- "going" (see venue).