To while away is to pass time pleasantly with nothing important to do. While away an afternoon.
It is warm where kill time is flat, which is the whole difference. The while in it is the old noun for a stretch of time rather than the conjunction.
1phrasewhile awayTo pass time pleasantly with nothing important to do.
“They would while away a whole Sunday over one newspaper.”
while away is a phrase.
Practised in Phrasal Verbs