Nonsense poet’s lecherous look, they say (4)
I believe the answer is:
lear
'nonsense poet's' is the definition.
(Edward Lear wrote nonsense poetry)
'lecherous look they say' is the wordplay.
'lecherous look' becomes 'leer' (leer can mean a lecherous or suggestive look).
'they say' shows a homophone (sound like).
'leer' sounds like 'LEAR'.
(Other definitions for lear that I've seen before include "A real playful king" , "Tragic Shakespearian king" , "The Bard's foolish king" , "Tragic Shakespearean king" , "Mad king" .)