The Collaborative International Dictionary of English v.0.48:

Lok \Lok\ (l[o^]k), Loki \Lo"ki\ (l[=o]"k), n. [Icel. Loki,
   perh. akin to lokka, locka to allure, entice.] (Scandinavian
   Myth.)
   The evil deity, the author of all calamities and mischief,
   answering to the Ahriman of the Persians.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Loki
    n 1: (Norse mythology) trickster; god of discord and mischief;
         contrived death of Balder and was overcome by Thor

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "Loki":
   Aesir, Aides, Aidoneus, Balder, Bor, Bori, Bragi, Cerberus, Charon,
   Cora, Despoina, Dis, Dis pater, Donar, Erebus, Forseti, Frey,
   Freya, Freyja, Freyr, Frigg, Frigga, Hades, Heimdall, Hel, Hertha,
   Hoenir, Idun, Ing, Ithunn, Kore, Minos, Nanna, Nemesis, Nerthus,
   Njord, Njorth, Odin, Orcus, Osiris, Persephassa, Persephone, Pluto,
   Proserpina, Proserpine, Reimthursen, Rhadamanthus, Satan, Set, Sif,
   Sigyn, Thor, Tiu, Typhon, Tyr, Ull, Ullr, Vali, Vanir, Vidar,
   Vitharr, Wayland, Weland, Woden, Wotan, Wyrd