Singer seen in national tour (4)
I believe the answer is:
alto
'singer' is the definition.
(alto is a kind of singer)
'in national tour' is the wordplay.
'in' indicates a hidden word.
'ALTO' is hidden in the letters of 'national tour'.
'seen' is the link.
(Other definitions for alto that I've seen before include "The highest adult male singing voice" , "Singing voice between tenor and soprano" , "Second of four parts (in singing)" , "High male singing voice" , "The highest adult male singing-voice" .)