Mos \Mos\, n., sing. of Mores.
Source: Webster's Revised Unabridged Dictionary (1913)
Mores \Mo"res\ (m[=o]"r[=e]z), n. pl.; sing. Mos (m[=o]s). [L.] Customs; habits; esp., customs conformity to which is more or less obligatory; customary law.