Alto singer disturbed by tenor is most annoyed (8)
I believe the answer is:
angriest
'most annoyed' is the definition.
(I've seen this before)
'alto singer disturbed by tenor' is the wordplay.
'alto' becomes 'a' (musical abbreviation).
'disturbed' indicates anagramming the letters (the order of letters is disturbed).
'by' says to put letters next to each other.
'tenor' becomes 't' ().
'a'+'singer'='asinger'
'asinger' is an anagram of 'angries'.
'angries'+'t'='ANGRIEST'
'is' acts as a link.
(Other definitions for angriest that I've seen before include "Most wrathful" , "Extremely mad" , "Most characteristic of 1950s young men" , "Most annoyed or hostile" , "Most incensed kind of ingrates" .)