More exactly a nickname, of Antigonos III, regent and king of Macedonia 229-221 BCE.
The word is conventionally regarded as the future participle of the verb di/dwmi ("I give"); Plutarch, Life of Aemilius Paulus 8.3, states that this was intended to designate him a man of promises which he failed to keep; so likewise e.g. R.M. Errington in OCD(4) 102 s.v. 'Antigonus(3)'. Since this Antigonos apparently had another epithet, Guardian (Livy 40.54.5; Athenaeus, Deipnosophists 6.251D [6.58 Kaibel]), Hammond & Walbank regard it as possible that dw/swn is a Macedonian word with that meaning (so already K.J. Beloch); and they dismiss what Plutarch says as "a poor guess, for Antigonus did hand over the kingdom to [the legitimate heir] Philip on his death."