Source : Webster's Revised Unabridged Dictionary (1913)

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.

         The ethical meaning of the miracles.     --Trench.

   {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?

Source : WordNet®

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: {moral principle},
           {value-system}, {value orientation}]
     2: a system of principles governing morality and acceptable
        conduct [syn: {ethical code}]