Dictionary of Medieval Names
from European Sources

Llywellyn m. Lugus, the name of a Celtic deity, deriving from Proto-Celtic *lug, of disputed meaning, + Belenus, the name of a Celtic sun deity, of uncertain origin, possibly relating to the god-name Apollo.

The name of a 10th C king of Powys, an 11th C king of Gwynedd, Powys, and Deheubarth, a 12th-13th C prince of Gwynedd, a 13th C prince of Gwynedd, a 13th C king of Wales, a 13th C prince of Gwynedd.

This name became increasingly popular in Wales after the reign of Llywelyn the Great in the 12th-13th C, so much so that when Shakespeare needed to name a generic Welsh captain in Henry V, he named him Fluellen, a roughly phonetic version of the English pronunciation of Llywellyn. From the 13th C on, Anglo-Norman scribes often equated the name with Lewis (cf. Louis).

England
Latin
1281 Lewelini (gen) CHAMont-1 p. 45
Early Modern English
1558 Llewelyn RegSASel p. 2; 1559 Llewelyn ibid. p. 5; 1560 Llewelyn ibid. p. 5; 1560/1 Llewelyn ibid. p. 7
Wales
Latin
1198 Lowelin (nom) Pryce-1st no. 8; 1216xc1226 Lewelini (gen) ibid. no. 16, Lewelinus (nom) ibid. no. 16; 1223 Leulini (gen) ibid. no. 19, Leulinum (acc) ibid. no. 19; 1247 lewelyno (abl) ArchCambIII p. 228; 1452 Llewelyn (nom) ibid. p. 71; 1453 Llewellyn (nom) ibid. p. 69, Llewelyn (nom) ibid. p. 69; 1454 Llewelyn (nom) ibid. p. 71; 1455 Llewelyn (nom) ibid. p. 72; 1456 Llewelyn (nom) ibid. p. 258; 1457 Llewelyn (nom) ibid. p. 259
Early Modern English
1576 Lle'n RegLlantrithyd p. 61
Cite as: S.L. Uckelman. "Llywellyn". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2016, no. 4. http://dmnes.org/2016/4/name/Llywellyn.