Killing in self-defense is still murder, but it is "justified" under the circumstances and thus isnt morally culpable murder.
I think the word you are looking for is "homicide". Homicide is the killing of another human being. Murder is the illegal
killing of another human being. Killing another human being in self-defense would be "justifiable homicide," not murder... at least according to my dictionary.
Please let me clarify a few of my thoughts:
1. If you wish to use the word "murder" to add emotional strength to your argument, I won't disagree, I just don't think it is precise.
2. Even if killing animals is not murder, that doesn't make it right. I just think that a new concept is needed, similar to the concept of murder, which applies to animals. This concept, if it is to carry weight amongst the general public, must be rigorously explored and rationally defended.
3. I never suggested that eating plants was murder. I was merely pointing out that "death" could not solely be used as a standard of value. As Natalie pointed out, setience
is an important distinction between plants and animals. I would go a step further and argue that self-sentience
(or self-consciousess) represents a dividing line between the higher animals and the lower ones. It is not obvious to me that "sentience" is more important than "self-sentience" when deciding what to kill and what not to kill.
4. I totally agree that it is on the self-conscious level that the question of morality arises. So, no, morality does not apply to animals.