The Collaborative International Dictionary of English v.0.48:

Ethic \Eth"ic\, Ethical \Eth"ic*al\, a. [L. ethicus, Gr. ?, fr.
   ? custom, usage, character, dwelling; akin to ? custom, Goth.
   sidus, G. sitte, Skr. svadh?, prob. orig., one's own doing;
   sva self + dh? to set: cf. F. ['e]thique. See So, Do.]
   Of, or belonging to, morals; treating of the moral feelings
   or duties; containing percepts of morality; moral; as, ethic
   discourses or epistles; an ethical system; ethical
   philosophy.
   [1913 Webster]

         The ethical meaning of the miracles.     --Trench.
   [1913 Webster]

   Ethical dative (Gram.), a use of the dative of a pronoun to
      signify that the person or thing spoken of is regarded
      with interest by some one; as, Quid mihi Celsus agit? How
      does my friend Celsus do?
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

ethic \eth"ic\ ([e^]th"[i^]k), n.
   1. the principles of right and wrong that are accepted by an
      individual or a social group; as, the Puritan ethic.
      [WordNet sense 1]

   Syn: moral principle, value-system, value orientation.
        [WordNet 1.5]

   2. a system of principles governing morality and acceptable
      conduct. [WordNet sense 2]

   Syn: ethical code.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

ethic
    n 1: the principles of right and wrong that are accepted by an
         individual or a social group; "the Puritan ethic"; "a
         person with old-fashioned values" [syn: ethic, moral
         principle, value-system, value orientation]
    2: a system of principles governing morality and acceptable
       conduct [syn: ethic, ethical code]