The messenger left a note at the entrance (6)
I believe the answer is:
legate
'the messenger' is the definition.
(I've seen this before)
'left a note at the entrance' is the wordplay.
I cannot quite see how this works, but
'left' could be 'leg' (left leg) and 'leg' is found within the answer.
'a' is present in the answer.
'note' could be 'te' (musical note as in do re mi fa so la ti) and 'te' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for legate that I've seen before include "Envoy, maybe papal" , "messenger for the Pope" , "Envoy representing the Pope" , "Vatican emissary" , "One being tested" .)