What’s almost too nice to put in your gin? (5)

I believe the answer is:
tonic
'put in your gin?' is the definition.
I can't tell whether this defines the answer.
'what's almost too nice' is the wordplay.
'what's almost' means to remove the last letter (almost the whole word is kept).
'nice' becomes 'nic' (I can't explain this - if you can you should give a lot more credence to this answer).
'too' with its final letter taken off is 'to'.
'to'+'nic'='TONIC'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for tonic that I've seen before include "something medicinal" , "Invigorating medicine - keynote" , "something nice and fresh" , "Stimulus" , "shot in the arm" .)
