Speech written on an envelope (7)
I believe the answer is:
address
'speech' is the definition.
(synonyms)
'written on an envelope' is the wordplay.
I cannot really understand how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found within the answer.
'an' could be 'a' and 'a' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for address that I've seen before include "hail maybe?" , "directions in window" , "personal details" , "Talk - indication of house" , "Place of abode" .)