Part coolish, otherwise boiling (3)
I believe the answer is:
hot
'boiling' is the definition.
(similar in meaning)
'part coolish otherwise' is the wordplay.
'part' says the answer is hidden in the clue.
'HOT' is hidden within 'coolish otherwise'.
(Other definitions for hot that I've seen before include "recently stolen" , "Fiery" , "'Strike while the iron is ...'" , "SECOND PART OF 11" , "Radioactive; very warm" .)