Apparently from Proto-Indo-European *ser- + *-wos, but the exact sense of the root *ser- from which *serwos derives is uncertain. Either: “to bind”, in...
*ser- to guard Terms derived from the Proto-Indo-European root *ser- (guard) (3 c, 0 e) *ser-wo-s Proto-Italic: *serwos (or perhaps from the sense “to bind”...