Favourable purchase, we hear, is the last word (7)
I believe the answer is:
goodbye
'word' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'favourable purchase we hear is the last' is the wordplay.
'favourable' becomes 'good' (associated in meaning).
'purchase' becomes 'buy' (buy is a kind of purchase).
'we hear' indicates a 'sounds like' (homophone) clue.
'last' says to take the final letters.
The last letter of 'the' is 'e'.
'buy' sounds like 'by'.
'good'+'by'+'e'='GOODBYE'
Can you help me to learn more?
(Other definitions for goodbye that I've seen before include "6 Down" , "Farewell remark" , "Adieu" , "so long" , "Cheers" .)