dictionaries are in general never " universal" 100% there are always some variances on certain definitions, though usually subtle.
Taking a life, to me is horrid, with very very little room for reasons... That said I also know that " at times" it's necessary. The protection of self, or others, be it in the moment, or in the long run are the ones I can typically accept, and approve of... it's those situations where there was no other real option.
Doing so as a statement, to establish a atmosphere of fear, doing it out of lust, or passion, or as an addiction to the rush (addicted to things mentioned before), to intentionally cause suffering on others, be it the victim, or those around them is where it's unforgivable
Doing it as a solider is different than the other two, in the sense that it " tends" to be for the protection of ideals. I may not always agree with it, of find it justified, but Im also of the mind to know that it's unavoidable... and " most often" it's soldier to solider... though wanton destruction of civilians no longer is military in my mind, and become murder. ( granted there are situations of misidentified persons)
So I guess, like they all said: the reasons/context behind it are a major factor. I would die, and kill to protect my children, or really anyone child or not if it was necessary...what constitutes as necessary really is a fine line though based on what they are being protected from.
I'd be pretty shocked if somebody I knew killed someone. It would really depend on when, and how, and why. If it was murder, sure, I'd still love them, but I'd also turn them in.