A form of the name is the Welsh Arwen.
Arwyn is not often used as a baby girl name. It is not in the top 1000 names.
Baby names that sound like Arwyn include Ariene (English), Arin (English), Arinne (Gaelic), Armagan (Turkish), Arman, Arna (Hebrew), Arni (Hebrew), Arnine, Arnon, Arnyah, Arwen (Welsh), Aryn, Aryne, Arynn, Arynne, Eireen (English, Gaelic, and Irish), Eirin, Eirinn, Ireen (English), and Ireene (English).
† English pronunciation for Arwyn: AA as in "odd (AA.D)" ; R as in "race (R.EY.S)" ; W as in "we (W.IY)" ; IH as in "it (IH.T)" ; N as in "knee (N.IY)"