Vowels heard in comfort (4)
I believe the answer is:
ease
'comfort' is the definition.
(I know that comfort can be written as ease)
'vowels heard in' is the wordplay.
'vowels' becomes 'ee' (E is a vowel).
'heard' becomes 'as' (I am not sure about this - if you are sure you should believe this answer much more).
'in' means one lot of letters goes inside another.
'ee' placed around 'as' is 'EASE'.
Can you help me to learn more?
(Other definitions for ease that I've seen before include "'Comfort, rest (4)'" , "State of relaxation or rest" , "Absence of hardship" , "Reduce (pain)" , "composure" .)