One sax used in national tour (4)
I believe the answer is:
alto
'one sax' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'in national tour' is the wordplay.
'in' indicates a hidden word.
'ALTO' is hidden within 'national tour'.
'used' acts as a link.
Can you help me to learn more?
(Other definitions for alto that I've seen before include "Second of four parts (in singing)" , "Voice part" , "The highest adult male singing voice" , "Singer's hidden inside chemical toilet" , "Singing range" .)