That backward business before blast-off (9)
I believe the answer is:
countdown
'blast-off' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I don't see?
'that backward business before' is the wordplay.
I cannot quite see how this works, but
'business' could be 'co' (short for company) and 'co' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for countdown that I've seen before include "game show" , "TV quiz show" , "5-4-3-2-1" , "programme on the box" , "Three, two, one - launch spacecraft" .)