Fear old man's about to be imprisoned (5)

I believe the answer is:

dread

I'm a little stuck... Click here to teach me more about this clue!

'fear' is the definition.
(synonyms)

'old man's about to be imprisoned' is the wordplay.
'old man' becomes 'dad' (synonyms).
'about' is an insertion indicator.
'to be imprisoned' becomes 're' (I can't explain this - if you can you should believe this answer much more).
'dad' placed around 're' is 'DREAD'.

Can you help me to learn more?

(Other definitions for dread that I've seen before include "Awe" , "alarm" , "Fear - dire" , "Trepidation" , "Frightful" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.