Ambassador carrying round garden tool (3)
I believe the answer is:
hoe
'garden tool' is the definition.
(I've seen this before)
'ambassador carrying round' is the wordplay.
'ambassador' becomes 'he' (His or Her Excellency).
'carrying' is an insertion indicator.
'round' becomes 'o' (round can mean a round object).
'he' placed around 'o' is 'HOE'.
(Other definitions for hoe that I've seen before include "Attend to beds" , "Purple gem" , "Plymouth - -" , "Use garden tool" , "Weeding implement" .)