A grass we’ve heard is crooked (4)
I believe the answer is:
awry
'crooked' is the definition.
(similar in meaning)
'a grass we've heard' is the wordplay.
'grass' becomes 'rye' (I've seen this before).
'we've heard' shows a homophone (sound like).
'rye' is a homophone of 'wry'.
'a'+'wry'='AWRY'
'is' is the link.
(Other definitions for awry that I've seen before include "Askance, askew" , "Uneven, crooked" , "Amiss, askew" , "Off-centre" , "Crookedly" .)