He's the boss, dear fellow (3,3)
I believe the answer is:
old man
'fellow' is the definition.
(thesaurus)
'he's the boss dear' is the wordplay.
I cannot quite see how this works, but
'he' could be 'man' (I've seen this in another clue) and 'man' is found in the answer.
The remaining letters 'old' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for old man that I've seen before include "Aged male as informal father" , "Husband (inf)" , "Master?" , "Senior citizen" , "Boyfriend" .)