Speech that may be written on an envelope (7)
I believe the answer is:
address
'speech' is the definition.
(address is a kind of speech)
'written on an envelope' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' (regarding) and 're' is found within the answer.
'an' could be 'a' and 'a' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'that may be' is the link.
Can you help me to learn more?
(Other definitions for address that I've seen before include "Treat" , "Speak formally to an audience" , "Art" , "Deliver a speech" , "Begin to deal with" .)