"Groom" in Marriage?

Groom for me as I know it means a man who tends to the horses, or and in the verb form, it is to take care of one's appearance. Then, why is it used to refer to the man of the marriage? Is there any etymological reasons?

Solution 1:

groom (n.1) c.1200, grome "male child, boy;" c.1300 as "youth, young man." 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.). Meaning "male servant who attends to horses" is from 1660s.

groom (n.2) husband-to-be at a wedding, c.1600, short for bridegroom, in which the second element is O.E. guma "man."

groom (v.) 1809, from groom (n.1) in its secondary sense of "male servant who attends to horses;" 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. Related: Groomed; grooming.

That's what EtymOnline gives for the groom. It seems these are two different words with same spelling and pronunciation.

Solution 2:

As Etymonline reports, groom in the meaning of “husband-to-be at a wedding” is circa 1600. It is a shortening of bridegroom. Bridegroom itself is earlier, from the Old English brydguma (suitor), from bryd (bride) + guma (man). The Old English brydguma ending was altered in the 16th century to align with groom (in the sense of “boy”, “lad”).

It's nice to note that it's reportedly the only word in which the Old English guma (man) is still present. This guma, which comes from Proto Germanic guman, was displaced by its cognate human, from Middle French humain, from Latin humanus.