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]

WordNet (r) 3.0 (2006):

ethical
    adj 1: of or relating to the philosophical study of ethics;
           "ethical codes"; "ethical theories"
    2: conforming to accepted standards of social or professional
       behavior; "an ethical lawyer"; "ethical medical practice";
       "an ethical problem"; "had no ethical objection to drinking";
       "Ours is a world of nuclear giants and ethical infants"- Omar
       N. Bradley [ant: unethical]
    3: adhering to ethical and moral principles; "it seems ethical
       and right"; "followed the only honorable course of action"
       [syn: ethical, honorable, honourable]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "ethical":
   Christian, axiological, blameless, clean, conscientious, correct,
   creditable, decent, deferential, duteous, dutiful, elevated, erect,
   estimable, ethological, fair, full of integrity, good, high-minded,
   high-principled, highly respectable, honest, honorable, immaculate,
   inviolate, irreproachable, just, law-abiding, law-loving,
   law-revering, manly, moral, moralistic, noble, obedient, observant,
   open, principled, proper, pure, reputable, respectable, respectful,
   right, right-minded, righteous, scrupulous, spotless, stainless,
   sterling, straightforward, true-dealing, true-devoted,
   true-disposing, true-souled, true-spirited, truehearted,
   unblemished, uncorrupt, uncorrupted, undefiled, unimpeachable,
   unspotted, unstained, unsullied, untarnished, upright, uprighteous,
   upstanding, virtuous, worthy, yeomanly