Chorus section (6)
(Other definitions for tenors that I've seen before include "Male singers from Reston" , "Male singing voices" , "Male singers with high register" , "Opera singers" .)
'chorus section' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for altos that I've seen before include "Lowest female singing voices" , "Choir members" , "Females who sing in the lowest range" , "Highest male, lowest female, voices" , "High male or low female voices" .)