Frightened so end up using my pen-name (9)
I believe the answer is:
pseudonym
'pen-name' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for pseudonym that I've seen before include "Our cryptic crossword always carries one" , "Pen-name" , "Goliath, for one" , "Fictitious name used by author" , "Cinephile, for one" .)