A town on the tube (5)
I believe the answer is:
acton
'tube' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's an association between them I don't understand?
'a town on the' is the wordplay.
'town' becomes 'con' (I can't justify this - if you can you should give a lot more credence to this answer).
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'con' enclosing 't' is 'cton'.
'a'+'cton'='ACTON'
Can you help me to learn more?
(Other definitions for acton that I've seen before include "Gladstone's adviser" , "Part of the London borough of Ealing - British historian, d. 1902" , "part of London on the tube" , "somewhere in London" , "District of West London" .)