Come together with ambassador in centre (6)
I believe the answer is:
cohere
'come together' is the definition.
(I've seen this in another clue)
'ambassador in centre' is the wordplay.
'ambassador' becomes 'HE' (His or Her Excellency).
'in' is an insertion indicator.
'centre' becomes 'core' (core can mean something's centre).
'he' placed within 'core' is 'COHERE'.
'with' is the link.
(Other definitions for cohere that I've seen before include "Hang together" , "Cling" , "Form a whole" , "Stick or hold together and resist separation" , "Hold firmly together" .)