i am convinced

severus. sever us.

dumbledore's last words: severus. severus please.

it was a command, a request, for snape to sever dumbledore's life.

it was a sacrifice snape didn't want to make: he didn't want to commit murder, he didn't want to be hunted for murder, and he didn't want dumbledore to die. he was the one who had to kill dumbledore, though, for several reasons.

many of the given and surnames in harry potter have meanings:

lupin from lupis -- wolf
slughorn -- a fat slug
sirius black -- black dog
neville longbottom -- a kind of tea leaf
voldemort -- flying death (i think that's what that one means) or it could mean returning from death... or flying from death... vol de mort
malfoy -- mal = bad

dumbledore -- i think 'dumb' might be about how little he ever tells anyone, he operates on a
need to know basis.

and so why can't 'severus' be directly taken to mean 'sever us'?

i think that at the end, when snape is escaping with malfoy, he is still instructing harry... first of all, he saves harry's life by reminding other death-eaters of their orders to leave harry for voldemort himself... but then as snape duels with harry and snape blocks every spell harry tries, he says "blocked again and again until you learn to keep your mouth shut and your mind closed"

until harry learns this skill of occlumency, he will never stand a chance against voldemort. snape wants harry to improve his occlumency skills.