Terrible fear in turkey, seeing gull (7)
I believe the answer is:
defraud
'gull' is the definition.
(thesaurus)
'terrible fear in turkey' is the wordplay.
'terrible' indicates an anagram.
'in' indicates putting letters inside.
'turkey' becomes 'dud' (synonyms).
'fear' is an anagram of 'efra'.
'efra' inserted inside 'dud' is 'DEFRAUD'.
'seeing' acts as a link.
(Other definitions for defraud that I've seen before include "Deprive of by deceit" , "Diddle" , "Cheat, deceive" , "Get money from (someone) by deception" , "Illegally get money from (someone)" .)