Fear about to transfix old man (5)
I believe the answer is:
dread
'fear' is the definition.
(I know that dread is a type of fear)
'about to transfix old man' is the wordplay.
'about' means one lot of letters goes inside another.
'to transfix' becomes 're' (I am not sure about this - if you are sure you should believe this answer much more).
'old man' becomes 'dad' (both can mean one's father).
're' placed into 'dad' is 'DREAD'.
Can you help me to learn more?
(Other definitions for dread that I've seen before include "Terrible fear" , "Affright" , "Be very averse to" , "Hairstyle" , "Great fear or apprehension" .)