sir [ME] A shortened form of sire [ME] that has been a title for a knight since the Middle Ages. Kings were formerly addressed as sire, though now the term is more often used for the male parent of an animal. Sire is from Latin senior [ME] ‘older, older man’, related to senex ‘old, old man’, from which senate [ME] and senile [M17th] also derive. In languages descended from Latin, words based on senior often became the way of addressing a man, for example señor in Spanish, signor in Italian, and the second element of monsieur in French.