Mouth-watering ice-cream's first in rescue (10)
I believe the answer is:
salivation
'mouth-watering ice-cream's first in rescue' is the definition.
I can't judge whether this defines the answer.
'cream's first in rescue' is the wordplay.
'cream's first' becomes 'i' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'rescue' becomes 'salvation' (salvation is a kind of rescue).
'i' inserted within 'salvation' is 'SALIVATION'.
Can you help me to learn more?
(Other definitions for salivation that I've seen before include "sign of hunger" , "preparation for eating" , "Sign of anticipation" , "Signs of expecting lunch" .)