Command from top to carry explosive (6)
I believe the answer is:
behest
'command' is the definition.
(behest is a kind of command)
'top to carry explosive' is the wordplay.
'top' becomes 'best' (associated in meaning).
'to carry' means one lot of letters goes inside another.
'explosive' becomes 'he' (abbreviation for high explosive).
'best' going around 'he' is 'BEHEST'.
'from' is the link.
(Other definitions for behest that I've seen before include "Command - Thebes (anag)" , "Command, bidding" , "(At someone's) command" , "Order" .)