The only free and comprehensive online etymological dictionary of the Spanish language
matrimonio m. (Noun) "matrimony"
14th cent. Borrowed from Latin matrimonium 'id.' Literally a "mother-obligation." From matr- "mother" (see madre) and -monium "obligation" (see -monio).
Indo-European
Romance
Portuguese matrimónio, Catalan matrimoni, Italian matrimonio, Romanian matrimoniu

"“Marriage” has no Indo-European term. In speaking of the man it is simply said—and this in expressions which have often been remodeled in particular languages—that he “leads” (home) a woman whom another man has “given” him (Lat. uxorem ducere and nuptum dare; in speaking of the woman, that she enters into the “married state,” receiving a function rather than accomplishing an act (Lat. ire in matrimonium)." ~ E. Benveniste, Indo-European Language and Society (1973)

"No single term for 'marriage' can be reconstructed; different legal kinds of marriage were recognized, including marriage by abduction... In the daughter languages, 'to marry' (a woman) is usually expressed by a verb meaning 'to lead away' or 'to take' (as Latin uxorem ducere 'lead a wife, marry'), and this can be confidently projected back onto the proto-language." ~ B. Fortson, Indo-European Language and Culture (2011)