Innocent? Need a definition

[o_mlly]

I am asking for the answer, thus the question.

Need more information to give an answer.

i.e., the act, moral object, intent, circumstances.

 

[goout]

It is a usual argument that intentionally killing an “innocent” person is always, under any condition an unethical (immoral) action. Unfortunately the word “innocent” is undefined. Can anyone provide a rigorous definition for it?

How do you define"rigorous"?