A fellow diner-out: someone pleasant to be with (6)
I believe the answer is:
friend
'someone pleasant to be with' is the definition.
I can't judge whether this definition defines the answer.
'a fellow diner-out' is the wordplay.
'a fellow' becomes 'f' (abbreviation - of a society etc.**).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'diner' anagrammed gives 'riend'.
'f'+'riend'='FRIEND'
Can you help me to learn more?
(Other definitions for friend that I've seen before include "China" , "Companion; Quaker" , "Member of religious society" , "Associate, supporter" , "One in need is one indeed" .)