The Collaborative International Dictionary of English v.0.48:

Lex \Lex\ (l[e^]ks), n.; pl. Leges (l[=e]"j[=e]z). [L. See
   Legal.]
   Law; as, lex talionis, the law of retaliation; lex terr[ae],
   the law of the land; lex fori, the law of the forum or court;
   lex loci, the law of the place; lex mercatoria, the law or
   custom of merchants.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "lex":
   act, bill, bylaw, canon, decree, dictate, dictation, edict,
   enactment, form, formality, formula, formulary, institution, jus,
   law, legislation, measure, ordinance, ordonnance, prescript,
   prescription, regulation, rubric, rule, ruling, standing order,
   statute