Tired Shakespearean king stuck in past (6)
I believe the answer is:
bleary
'tired' is the definition.
(similar in meaning)
'shakespearean king stuck in past' is the wordplay.
'shakespearean king' becomes 'Lear' (King Lear).
'stuck in' means one lot of letters goes inside another.
'past' becomes 'by' (as in years gone by).
'lear' inserted into 'by' is 'BLEARY'.
(Other definitions for bleary that I've seen before include "Dim" , "not clear" , "Indistinct - hazy in outline" , "Eyes like this are dull from exhaustion" , "Smudged, indistinct" .)