groom (n.1) Look up groom at Dictionary.com
c.1200, grome "male child, boy;" c.1300 as "youth, young man." No known cognates in other Germanic languages. Perhaps from Old English *groma, related to growan "grow;" or from Old French grommet "servant" (compare Middle English gromet "ship's boy," early 13c.). Meaning "male servant who attends to horses" is from 1660s.
groom (n.2) Look up groom at Dictionary.com
husband-to-be at a wedding, c.1600, short for bridegroom, in which the second element is Old English guma "man."
groom (v.) Look up groom at Dictionary.com
1809, from groom (n.1) in its secondary sense of "male servant who attends to horses." Transferred sense of "to tidy (oneself) up" is from 1843; figurative sense of "to prepare a candidate" is from 1887, originally in U.S. politics. Related: Groomed; grooming.