The Collaborative International Dictionary of English v.0.48:

Nanna \Nanna\ n.
   1. The wife of Balder.
      [WordNet 1.5]

   2. (Sumerian mythology) The god of the moon; counterpart of
      the Akkadian Sin.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

nanna
    n 1: the mother of your father or mother [syn: grandma,
         grandmother, granny, grannie, gran, nan, nanna]
    2: (Norse mythology) wife of Balder
    3: god of the Moon; counterpart of the Akkadian Sin