If one returns a casual hug that will do (6)
I believe the answer is:
enough
'that will do' is the definition.
'if one returns a casual hug' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'one' is 'eno' which is present in the answer.
an anagram of 'hug' is 'ugh' which is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for enough that I've seen before include "Satisfactory quantity" , "The quantity needed, sufficient" , "` `A word to the wise is ......' '" , "To the required extent" , "As many as necessary" .)