Gutted Estonian to cheer up and act as informer (9)
I believe the answer is:
enlighten
'act as informer' is the definition.
(to enlighten someone is to give them information)
'gutted estonian to cheer up' is the wordplay.
'gutted' says to hollow out the word (remove centre letters) (to gut something is to remove its insides).
'to cheer up' becomes 'lighten' (to lighten up is to cheer up).
'estonian' with its centre removed is 'en'.
'en'+'lighten'='ENLIGHTEN'
'and' is the link.
(Other definitions for enlighten that I've seen before include "Edify" , "Impart knowledge to" , "Give information to" , "Educate, inform" , "Apprise" .)