In fact, a terrible follower (7)
I believe the answer is:
fanatic
'follower' is the definition.
(thesaurus)
'in fact a terrible' is the wordplay.
'terrible' indicates anagramming the letters.
'in'+'fact'+'a'='infacta'
'infacta' with letters rearranged gives 'FANATIC'.
(Other definitions for fanatic that I've seen before include "crank" , "Zealot or extremist" , "Person filled with excessive zeal for cause" , "Overzealous person" , "Excessively devoted" .)