Fear about to stop old man (5)
I believe the answer is:
dread
'fear' is the definition.
(I know that fear can be written as dread)
'about to stop old man' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to stop' means one lot of letters goes inside another (stopping can mean blocking a gap).
'old man' becomes 'dad' (both can mean one's father).
're' placed inside 'dad' is 'DREAD'.
(Other definitions for dread that I've seen before include "Terrible fear" , "Anticipate fearfully" , "Anticipate with horror" , "Terror" , "Affright" .)