Go up to plug explosive old weapon (7)
I believe the answer is:
trident
'old weapon' is the definition.
'trident' can be an answer for 'weapon' (trident is a kind of weapon). I'm unsure of the 'old' bit.
'go up to plug explosive' is the wordplay.
'go up' becomes 'ride' (riding is a kind of going up).
'to plug' means one lot of letters goes inside another (to plug can mean to block a gap within something).
'explosive' becomes 'tnt' (TNT is an example).
'ride' inserted inside 'tnt' is 'TRIDENT'.
Can you help me to learn more?
(Other definitions for trident that I've seen before include "Nuclear weapon" , "Pronged spear" , "Neptune's spear - missile" , "Neptune's fork" , "Spear held by Neptune or Britannia" .)