Criminal's caught out in scam (4)
I believe the answer is:
rook
'scam' is the definition.
(thesaurus)
'criminal's caught out' is the wordplay.
'criminal' becomes 'crook' (synonyms).
'caught' becomes 'c' (cricket abbreviation).
'out' indicates named letters should be taken away.
'crook' with 'c' taken out is 'ROOK'.
'in' acts as a link.
(Other definitions for rook that I've seen before include "Gregarious black bird" , "Use deceit to get money" , "Bird; playing piece" , "Chess piece also called castle" , "Poignant, evocative" .)