O.E. sunu "son," from P.Gmc. *sunuz (cf. O.S., O.Fris. sunu, O.N. sonr, Dan. søn, Swed. son, M.Du. sone, Du. zoon, O.H.G. sunu, Ger. Sohn, Goth. sunus "son"), from PIE *sunu-/*sunyu- (cf. Skt. sunus, Gk. huios, Avestan hunush, Armenian ustr, Lith. sunus, O.C.S. synu, Rus., Pol. syn "son"), from root *su- "to give birth" (cf. Skt. sauti "gives birth," O.Ir. suth "birth, offspring"). Sonny as a familiar form of address to one younger or inferior is from 1870. Son of _____ as the title of a sequel to a book or movie is recorded from 1929.