Ambassador transported top relic in conveyance (10)
I believe the answer is:
helicopter
'conveyance' is the definition.
(helicopter is a kind of conveyance)
'ambassador transported top relic' is the wordplay.
'ambassador' becomes 'HE' (His or Her Excellency).
'transported' indicates an anagram.
'top'+'relic'='toprelic'
'toprelic' with letters rearranged gives 'licopter'.
'he'+'licopter'='HELICOPTER'
'in' is the link.
(Other definitions for helicopter that I've seen before include "Rotary-winged craft" , "Rotorcraft" , "Flier" , "surveillance equipment" , "surveillance vehicle" .)