Online Etymology Dictionary

groom (2): husband-to-be at a wedding, 1604, short for bridegroom (q.v.), from O.E. guma "man."
groom (1): early 13c., grome "male child, boy, youth." No known cognates in other Germanic languages. Perhaps from O.E. *groma, related to growan "grow;" or from O.Fr. grommet "servant" (cf. M.E. gromet "ship's boy," early 13c.). The fact is, it appeared 13c. and nobody knows from whence. Meaning "male servant who attends to horses" is from 1660s. The verb is first attested 1809; the 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.
equerry: 1591, short for groom of the equirrie, from esquiry "stables," from M.Fr. escuerie, perhaps from M.L. scuria "stable," from O.H.G. scura "barn;" or from O.Fr. escuier "groom," from V.L. scutarius "shield-bearer." In either case, spelling infl. by L. equus "horse," to which it is not related.
bridegroom: O.E. brydguma "suitor," from bryd "bride" (see bride) + guma "man" (cf. O.N. gumi, O.H.G. gomo, cognate with L. homo "man"). Ending altered 16c. by folk etymology after groom "groom, boy, lad" (q.v.). Common Germanic compound (cf. O.S. brudigumo, O.N. bruðgumi, O.H.G. brutigomo, Ger. Bräutigam), except in Goth., which used bruþsfaþs, lit. "bride's lord."
marshal: early 13c., from O.Fr. mareschal, originally "stable officer, horse tender, groom" (Frankish L. mariscaluis) from Frank. *marhskalk, lit. "horse-servant" (cf. O.H.G. marahscalc "groom"), from P.Gmc. *markhaz "horse" (see mare (1)) + *skalkaz "servant" (cf. Du. schalk "rogue, wag," Goth. skalks "servant"). Cognate with O.E. horsþegn. For development history, cf. constable. The verb "to arrange for fighting" is from 1580s. Related: Marshaled.
constable: c.1200, from O.Fr. conestable, principal officer of the Frankish king's household, from L.L. comes stabuli, lit. "count of the stable" (established by Theodosian Code, c.438 C.E.), hence, "chief groom." Probably a translation of a Gmc. word. Meaning "an officer of the peace" is from c.1600, transferred to "police officer" 1836.
gift: c.1100, from O.N. gift, from P.Gmc. *giftiz (cf. O.Fris. jefte, M.Du. ghifte "gift," Ger. Mitgift "dowry"), from PIE base *ghabh- "to give or receive" (see habit). O.E. cognate gift meant "bride-price, marriage gift (by the groom), dowry" (O.E. for "giving, gift" was related giefu). Sense of "natural talent" is c.1300.
morganatic: 1727, from Fr. morganatique, from M.L. matrimonium ad morganaticam "marriage of the morning," probably from O.H.G. *morgangeba (M.H.G. morgengabe) "morning gift," corresponding to O.E. morgengifu (see morn + gift). In an unequal marriage between a man of royal blood and a common woman, this was a gift traditionally given to the wife on the morning after consummation, representing the only share she and her children may claim in the husband's estate. Also known as left-handed marriage, because the groom gives the bride his left hand instead of his right, but sometimes this latter term is used of a class of marriage (esp. in Germany) where the spouse of inferior rank is not elevated, but the children inherit rights of succession.
henchman: 1360, hengestman "high-ranking servant," originally "groom," from man + O.E. hengest "horse, stallion, gelding," from P.Gmc. *khangistas (cf. O.Fris. hengst, Du. hengest, Ger. Hengst "stallion"), probably lit. "best at springing," from PIE *kenku- (cf. Gk. kekiein "to gush forth;" Lith. sokti "to jump, dance;" Breton kazek "a mare," lit. "that which belongs to a stallion"). Became obsolete, but retained in Scottish as "personal attendant of a Highland chief," in which sense Scott revived it in literary Eng. in 1810. Sense of "obedient or unscrupulous follower" is first recorded 1839, probably based on a misunderstanding of the word as used by Scott.