Unambiguous about king in play (5)
I believe the answer is:
clear
'unambiguous' is the definition.
(associated in meaning)
'about king in play' is the wordplay.
'about' becomes 'c' (circa).
'king in play' becomes 'Lear' (Shakespeare's King Lear).
'c'+'lear'='CLEAR'
(Other definitions for clear that I've seen before include "School near Windsor" , "Lucid; to empty" , "Evident" , "Exculpate" , "Plain; unblock" .)