Hollow found in grains in cereal (9)
I believe the answer is:
insincere
'hollow' is the definition.
('insincere' can be similar in meaning to 'hollow')
'in grains in cereal' is the wordplay.
'in' indicates a hidden word.
'INSINCERE' is hidden within 'grains in cereal'.
'found' is the link.
(Other definitions for insincere that I've seen before include "tricky" , "Dissembling" , "Not genuine, feigned" , "Less than honest" , "Hollow" .)