Pressure inside Venus or a wildly exploding star (9)
I believe the answer is:
supernova
'exploding star' is the definition.
(I've seen this in another clue)
'pressure inside venus or a wildly' is the wordplay.
'pressure' becomes 'p' (abbreviation).
'inside' indicates putting letters inside.
'wildly' indicates an anagram.
'venus'+'or'+'a'='venusora'
'venusora' is an anagram of 'suernova'.
'p' going within 'suernova' is 'SUPERNOVA'.
(Other definitions for supernova that I've seen before include "Star made brilliant by stellar explosion" , "Star that explodes and becomes extremely luminous" , "Exploding star that becomes much brighter" , "Star in decline" , "Exploding star that becomes extremely luminous" .)