Bernard Tanguy, Communes du Finistère, p 134:  Castrum Mons Relax, 1128; ecclesia S. Martini de Monte Relaxo, 1128; ecclesia Beati Melanii de Monte Relaxo, 1170; Mont Relays, XIIè; (in) Montereleis, 1217; Montrelès, 1296; Montrelez, 1352; Morloys, 1371; Morlais, 1376; Morelaiz, 1385; Mourlaix, 1455; Montrelaes, Montrelaix, Mourlaix, 1464; Montrolaes, Morlaix,1499; breton Montroulez.