Ethics is derived from the Greek word "ethos" which means 'character'. Etymologically, it usually refers to an individual's characters.
Morals comes from Latin (moralis) which means 'custom', and again from an etymological perspective, usually refers to a social custom, thus it's determined by the society, or by the group.
In practice, it's a very fine line and for many, I wouldn't be surprised if they draw any distinction between the two, but I take the position that morals are the principles and standards of behavior as established by the society, and ethics are the rules by which we as individuals, but those principles and standards into practice.
So to judge a behavior as being ethical would mean that the individual behavior is consistent with the standards established by the society.
Now to define society in this context gets very interesting because societies exist on many levels. The society may be just the immediate family, or the neighborhood, or a religious community, a professional organization, a nationality and so forth. And although our own ethics may not change, the standards by which our behavior is judged is dependant on which society making the judgment. That means that the same act can be considered ethical on one level, and at the same time be unethical on another level.
Good Luck
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As a circle of light increases so does the circumference of darkness around it. - Albert Einstein