Millions get notice to quit capital (6)
I believe the answer is:
madrid
'capital' is the definition.
(Madrid is an example)
'millions get notice to quit' is the wordplay.
'millions' becomes 'm' (abbreviation).
'get' is a charade indicator (letters next to each other).
'notice' becomes 'ad'.
'to quit' becomes 'rid' ('rid' can be a synonym of 'quit').
'm'+'ad'+'rid'='MADRID'
(Other definitions for madrid that I've seen before include "Spanish capital" , "Capital of Spain since 1561" , "Spanish city" , "European capital city" , "Spain's capital" .)