A cereal, we hear, that's crooked (4)
I believe the answer is:
awry
'crooked' is the definition.
(similar in meaning)
'a cereal we hear' is the wordplay.
'cereal' becomes 'rye' (rye is a kind of cereal).
'we hear' indicates a 'sounds like' (homophone) clue.
'rye' sounds like 'wry'.
'a'+'wry'='AWRY'
'that's' acts as a link.
(Other definitions for awry that I've seen before include "Wary but distorted." , "Wonky" , "Wary (anag.)" , "Twisted; distorted" , "Uneven, crooked" .)