Clergyman's tea not especially tasty (8)
I believe the answer is:
chaplain
'clergyman's' is the definition.
(chaplain is a kind of clergyman)
'tea not especially tasty' is the wordplay.
I cannot really understand how this works, but
'tea' could be 'cha' (cha is a type of tea) and 'cha' is found in the answer.
The remaining letters 'plain' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for chaplain that I've seen before include "'Member of the clergy, in a hospital, say (8)'" , "Clergyman attached to military unit" , "Armed services clergyman" , "Member of the clergy attached to an institution" , "Clergyman attached to an institution, such as the army" .)