What is the X in X-mas?
1650s, name of a boat race among gondoliers held on the Grand Canal in Venice, from Italian (Venetian dialect) regatta, literally "contention for mastery," from rigattare "to compete, haggle, sell at retail." [Klein's sources, however, suggest a source in Italian riga "row, rank," from a Germanic source and related to English row (v.).] The general meaning of "boat race, yacht race" is usually considered to have begun with a race on the Thames by that name June 23, 1775 (cf. OED), but there is evidence that it was used as early as 1768.