Writer in passage shows man-eater (8)
I believe the answer is:
cannibal
'man-eater' is the definition.
(synonyms)
'writer in passage' is the wordplay.
'writer' becomes 'nib' (something which writes).
'in' indicates putting letters inside.
'passage' becomes 'canal' (canal is a kind of passage).
'nib' placed inside 'canal' is 'CANNIBAL'.
'shows' is the link.
(Other definitions for cannibal that I've seen before include "Anthropophagite" , "One who eats its own species" , "One with odd eating habits" , "Eater of one's own kind" , "One eats human flesh" .)