The Collaborative International Dictionary of English v.0.48:

Ethnic \Eth"nic\, Ethnical \Eth"nic*al\, a. [L. ethnicus, Gr. ?,
   fr. ? nation, ? ? the nations, heathens, gentiles: cf. F.
   ethnique.]
   1. Belonging to races or nations; based on distinctions of
      race; ethnological.
      [1913 Webster]

   2. Pertaining to the gentiles, or nations not converted to
      Christianity; heathen; pagan; -- opposed to Jewish and
      Christian.
      [1913 Webster]

   3. of or pertaining to a group having a distinct racial,
      cultural, religious or linguistic character; as, ethnic
      differences within a population can cause civil war.
      [PJC]

   4. being a member of a distinct racial or cultural minority
      within a larger population; as, ethnic Chinese own most of
      the businesses in Indonesia.
      [PJC]

WordNet (r) 3.0 (2006):

ethnical
    adj 1: denoting or deriving from or distinctive of the ways of
           living built up by a group of people; "influenced by
           ethnic and cultural ties"- J.F.Kennedy; "ethnic food"
           [syn: cultural, ethnic, ethnical]