King Lear's middle daughter (5)
I believe the answer is:
regan
'king lear's middle daughter' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for regan that I've seen before include "better half of Cornwall" , "king's daughter" , "Princess" , "part of 1 25 [KING LEAR]" , "Shakespearean baddie" .)