Pressure on furious buccaneer (6)
I believe the answer is:
pirate
'buccaneer' is the definition.
(historical term for a pirate)
'pressure on furious' is the wordplay.
'pressure' becomes 'p' (abbreviation).
'on' says to put letters next to each other.
'furious' becomes 'irate' (I've seen this before).
'p'+'irate'='PIRATE'
(Other definitions for pirate that I've seen before include "Silver, perhaps" , "Hook", for example" , "Criminal on the high seas" , "not officially circulated" , "Illegally-copied (version)" .)