Fear about to occupy the old man (5)
I believe the answer is:
dread
'fear' is the definition.
('dread' can be a synonym of 'fear')
'about to occupy the old man' is the wordplay.
'about' becomes 're' (regarding**).
'to occupy' means one lot of letters goes inside another (I've seen this in other clues).
'the old man' becomes 'dad' ('dad' can be a synonym of 'old man').
're' going within 'dad' is 'DREAD'.
(Other definitions for dread that I've seen before include "Apprehensive fear" , "Dared to fear greatly" , "Be afraid of - anxiety" , "Terror" , "fright" .)