Oscar regularly visited T S Eliot in capital (4)
I believe the answer is:
oslo
'capital' is the definition.
(capital of Norway)
'oscar regularly visited t s eliot' is the wordplay.
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'regularly visited' means one should take alternating letters (letters are taken at regular intervals).
't'+'s'+'eliot'='tseliot'
The alternating letters of 'tseliot' are 'slo'.
'o'+'slo'='OSLO'
'in' acts as a link.
(Other definitions for oslo that I've seen before include "Capital often frozen" , "Norwegian city, formerly Kristiania" , "Nordic capital" , "Location" , "Norwegian capital" .)