A son; used in
compound names, to
indicate paternity, especially. Of the
illegitimate sons of kings and princes of the blood; as, Fitzroy, the son of the king; Fitzclarence, the son of the
duke of Clarence.
Origin: OF. Fils, filz, fiz, son, F. Fils, L. Filius. See Filial.
Source: Websters Vocabulary