Void seen after dizzying plunge (8)
I believe the answer is:
nosedive
'plunge' is the definition.
(nosediving is a kind of plunging)
'void seen after dizzying' is the wordplay.
'after' means one lot of letters go next to another.
'dizzying' indicates an anagram (I've seen 'dizzy' mean this).
'void'+'seen'='voidseen'
'voidseen' anagrammed gives 'NOSEDIVE'.
(Other definitions for nosedive that I've seen before include "plummet" , "sudden drop" , "steep fall" , "headlong plunge" , "fall precipitately" .)