c. 1200 (late 12c. in surnames), grome "male child, boy;" c. 1300, "a youth, young man," also "male servant, attendant, minor officer in a royal or noble household ranking higher than a page; a knight's squire." Of unknown origin; no certain cognates in other Germanic languages. Perhaps from an unrecorded Old English *grom, *groma, which could be related to growan "to grow," and influenced by guma "man." Or perhaps from or influenced by Old French grommet "boy, young man in service, serving-man" (compare Middle English gromet "ship's boy," early 13c.). As the title of an officer of the English royal house from mid-15c. Specific meaning "male servant who attends to horses and stables" is from 1660s, from earlier combinations such as horse-groom, Groom of the Stables, etc.
"husband-to-be at a wedding; newly married man," c. 1600 (usually as a correlative of bride), short for bridegroom (q.v.), in which the second element is Old English guma "man."
"tend or care for; curry and feed," 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.