Person of rank very depressed before blastoff (9)
I believe the answer is:
countdown
'blastoff' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'person of rank very depressed' is the wordplay.
I cannot quite see how this works, but
'person' could be 'count' (count is a kind of person) and 'count' is located in the answer.
'of' could be 'o' and 'o' is located in the answer.
This explanation may well be incorrect...
'before' acts as a link.
Can you help me to learn more?
(Other definitions for countdown that I've seen before include "5-4-3-2-1" , "It ends 2, 1, zero" , "Three, two, one - launch spacecraft" , "Run-up" , "game show" .)