Name one twice (3)
I believe the answer is:
ian
'name' is the definition.
'one twice' is the wordplay.
'one twice' means two replacements for 'one'.
'one' becomes 'i' (Roman numeral).
'one' becomes 'an' (I've seen this in other clues).
'i'+'an'='IAN'
(Other definitions for ian that I've seen before include "Botham or Chappell?" , "Sir - McKellen, actor" , "- Botham, cricketer" , "Scottish John" , "... Fleming, author of the Bond books" .)