The best, general definition of love I've come up with is: one's willingness to do what one truly considers best for another without regard for personal desires.
There are 2 things I should point out:
1) by "willingness to do" I mean that which will be done unless impossible or prevented by something external -- if I am willing to do X and X is possible then I will do X unless something or someone prevents me from doing it.
2) I say "truly considers best" to draw a distinction between the lazy "this is what I was told is best" or "I don't really know but I think this is best" and the more difficult "best" that is determined by effort, honesty, study, research, etc. Likewise, I disallow a "best" determined according to what the lover desires, or wants.
Is this a good (accurate, useful) definition?