Old English welig "willow," from Proto-Germanic *wel- (cognates: Old Saxon wilgia, Middle Dutch wilghe, Dutch wilg), probably from PIE *wel- (3) "to turn, roll," with derivatives referring to curved, enclosing objects, cognate with Greek helix (see volvox). The change in form to -ow (14c.) paralleled that of bellow and fellow. The more typical Germanic word for the tree is represented by withy.