Short for All-hallows' mass (“All-saints' mass”), ultimately continuing Old English ealra hālġena mæsse (literally “All Saints' mass”), equivalent to hallow (“saint”) + -mas.
- (archaic) All Saints Day, November 1
c. 1603–1604, Shakespeare, William, Measure for Measure, Act 2, Scene 1:
Pompey: And, I beseech you look into Master Froth here, / sir; a man of fourscore pound a year, whose father died / at Hallowmas. Was't not at Hallowmas, Master Froth?