I searched for one recently, because I was in a similar situation. I didn't search very thoroughly, and didn't find a definition I particularly liked. However, the Mayo Clinic seems to have a decent overview.
I told my friend anyway, and he said, "Oh, well... I don't see why that would change anything. I like you the way you are." He has rather alexithymic characteristics, we have been quite close (off and on) for about five years, and is familiar with AS. I can't say that this will be helpful for you at all, but perhaps starting a conversation with your friend about feelings (I know, weird) or communication may invite him to share his thoughts on the subject. I found AS easier to relate to my friend after he told me that he would like to be a cyborg, so "the outside matches the inside a little more."
I hope it goes well for you