Difficult old fellow at session, slightly deaf (4-2-7)
I believe the answer is:
hard-of-hearing
'slightly deaf' is the definition.
(I've seen this before)
'difficult old fellow at session' is the wordplay.
I cannot really see how this works, but
'difficult' could be 'hard' (synonyms) and 'hard' is found in the answer.
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is located in the answer.
'fellow' could be 'he' ('he' refers to a man) and 'he' is located in the answer.
'at' could be 'in' (synonymous in some cases - eg at school, in school) and 'in' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for hard-of-hearing that I've seen before include "Rather deaf" , "Somewhat deaf" , "Partially deaf" , "Struggling to pick up sounds" .)