The Collaborative International Dictionary of English v.0.48:

obiter dictum \obiter dictum\ ([o^]b"[i^]*t[~e]r d[i^]k"t[u^]m),
   n.; pl. obiter dicta ([o^]b"[i^]*t[~e]r d[i^]k"t[.a]).
   (Law),
   An incidental and collateral opinion uttered by a judge. See
   Dictum, n., 2
   (a) .
       [1913 Webster]

WordNet (r) 3.0 (2006):

obiter dictum
    n 1: an incidental remark [syn: obiter dictum, passing
         comment]
    2: an opinion voiced by a judge on a point of law not directly
       bearing on the case in question and therefore not binding
       [syn: obiter dictum, dictum]