London Town? It's on the tube! (5)
I believe the answer is:
acton
'tube' is the definition.
Both the answer and definition are singular nouns.
Maybe there's an association between them I don't understand?
'london town? it's on' is the wordplay.
'london town?' becomes 'act' (I can't justify this - if you can you should believe this answer much more).
'act'+'on'='ACTON'
'the' is the link.
Can you help me to learn more?
(Other definitions for acton that I've seen before include "Gladstone's adviser" , "English statesman" , "London area" , "part of London on the tube" , "Part of the London borough of Ealing - British historian, d. 1902" .)