Dim British king in play (5)
I believe the answer is:
blear
'dim' is the definition.
(I've seen this before)
'british king in play' is the wordplay.
I cannot quite see how this works, but
'british' could be 'b' (abbreviation e.g. in 'BBC') and 'b' is located in the answer.
'king' could be 'lear' (King Lear) and 'lear' is found within 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 blear that I've seen before include "Make (the eyes) dim" , "Blur" , "Baler (anag.)" , "Indistinct" , "Watery, blurred" .)