WordNet (r) 3.0 (2006):

mitzvah
    n 1: (Judaism) a precept or commandment of the Jewish law [syn:
         mitzvah, mitsvah]
    2: (Judaism) a good deed performed out of religious duty [syn:
       mitzvah, mitsvah]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "mitzvah":
   act of grace, act of kindness, benefaction, benefit, benevolence,
   benignity, blessing, canon, code, commandment, convention,
   courtesy, dictum, favor, form, formula, general principle,
   golden rule, good deed, good offices, good turn, grace, guideline,
   guiding principle, imperative, kind deed, kind offices, kindly act,
   kindness, labor of love, law, maxim, mercy, moral, norm,
   obligation, office, ordinance, principium, principle, regulation,
   rubric, rule, service, settled principle, standard, tenet, turn,
   working principle, working rule