Under pressure I almost pinched gun (6)
I believe the answer is:
pistol
'gun' is the definition.
(I know that pistol is a type of gun)
'under pressure i almost pinched' is the wordplay.
'under' says to put letters next to each other.
'pressure' becomes 'p' (abbreviation).
'almost' means to remove the last letter (most of the word but not all of it).
'pinched' becomes 'stole' (pinch can mean to steal).
'stole' with its final letter taken off is 'stol'.
'p' next to 'i' is 'pi'.
'pi'+'stol'='PISTOL'
(Other definitions for pistol that I've seen before include "Hand-held firearm" , "Small firearm" , "Rectangular" , "Shakespearean character" , "Hand weapon" .)