Inherited from Middle French luitin (“mischievous demon”), a variation (with change of suffix) of older luiton, luitun (“marine monster”), itself an alteration (probably after Old French luitier (“to fight”)) of Old French nuiton, which itself was an alteration (after nuit (“night”)) of Old French netun (“marine monster, in rivers and seas”), from Latin Neptunus (“the god Neptune”). Doublet of Neptune. The semantic shift from the Greco-Roman god to a sea monster then evil folkloric creature has its origin in Neptune being reinterpreted as a demon, and so his name was also genericized into a type of monstrous demon during the Christianization of Gaul.
Compare Old French gene (“mischievous fairy”) and Romanian zână (“fairy”), derived from Latin Diāna, and French ogre, from Latin Orcus (“the underworld; the god Pluto”). A sermon by Merovingian French bishop St. Eligius (died 659) advises against belief in Neptune, Diana, Orcus and Minerva.
lutin m (plural lutins)