Arbor comes from a word referring to a shady resting place in a garden or a park surrounded by climbing shrubs or vines, made out of latticework. It comes from Latin herba (grass, herb) derived from PIE *gʰreh₁- (to grow, become green). Arbor is also a mechanical term referring to a rotating shaft in a machine or a main support in a beam. The origin of this word comes from Latin arbor meaning “tree” via PIE root *h₃erdʰ- (to grow, high). Arbor is also a Latin word meaning “tree”.
Arbor is also an English surname though it originated as a variant spelling of Harbor (also spelled Arbour) which refers to a body of water along the shore deep enough to anchor ships though it can also be used to describe a shelter or refuge. The origin of the word comes from Old English herebeorg (shelter, refuge; military quarters) via Proto-Germanic *harjabergō (army shelter; refuge) which ultimately derives from a PIE source.