The suffix -ίδας (Ionic-Attic -ίδης) is often considered to have originally formed patronymics, and hence, by widening of sense, also family-, deme-, and other group-names (§1). As it is difficult to give an acceptable explanation for ‘x-ίδας’ starting from an original meaning ‘son of x’ (§2), I will propose here a new solution: -ίδας as patronymic is a restricted use of the original meaning ‘member of the clan, group of...’. The suffix is a complex of -ίδ- and -α-, both of pre-Greek origin (§3 & §4). The first is, among other things, attested in territorial and phyle-names: Φωκίς, ’AργoΛίς, ’OζoΛίς, Aαιντίς (φυΛε). The second denotes male inhabitants of a territory and members of a phyle: ’AργóΛας, ’OζóΛας;, Aιαντ;ίδες (member of the Attic phyle Aιαντίς) (§5). -ίδ- and â–“(α)δ- are allomorphs of the same pre-Greek suffix, and -δας is probably a more original form than -ίδας (§6)).