Greeting the ambassador will love (5)
I believe the answer is:
hello
'greeting' is the definition.
(hello is a kind of greeting)
'the ambassador will love' is the wordplay.
'the ambassador' becomes 'he' (His or Her Excellency).
'will' becomes 'll'.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'he'+'ll'+'o'='HELLO'
(Other definitions for hello that I've seen before include "Welcome" , "Conversation starter" , "Conventional word of greeting" , "Look at that" , "Introductory greeting" .)