Blunder and almost blow up? (4)
I believe the answer is:
goof
'blunder' is the definition.
('goof' can be a synonym of 'blunder')
'almost blow up?' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'blow up?' becomes 'gooff' (going off is a kind of blowing up).
'gooff' with its final letter taken off is 'GOOF'.
'and' is the link.
(Other definitions for goof that I've seen before include "boob" , "In slang, bungle or blunder" , "foolish error" , "(Make a) silly mistake" , "Foolish mistake" .)