Beset by awful dread, the fellow held fast (7)
I believe the answer is:
adhered
'held fast' is the definition.
('adhere' can be a synonym of 'hold fast')
'beset by awful dread the fellow' is the wordplay.
'beset by' indicates putting letters inside ('beset' could historically mean 'cover').
'awful' is an anagram indicator.
'the fellow' becomes 'he' ('he' refers to a man).
'dread' anagrammed gives 'adred'.
'adred' placed around 'he' is 'ADHERED'.
(Other definitions for adhered that I've seen before include "Stuck; glued" , "Stuck to, remained loyal" , "Showed sticking power" , "Stuck (to something)" , "Stuck - redhead (anag)" .)