Working a lot around noon with a key (5)
I believe the answer is:
tonal
'with a key' is the definition.
(I've seen this in another clue)
'working a lot around noon' is the wordplay.
'working' is an anagram indicator.
'around' means one lot of letters goes inside another.
'noon' becomes 'n' (abbreviation for noon).
'a'+'lot'='alot'
'alot' is an anagram of 'toal'.
'toal' placed around 'n' is 'TONAL'.
(Other definitions for tonal that I've seen before include "According to musical key" , "Alton (anag.)" , "It's wood can be used to make twenty three dn" , "Relating to conventional keys and harmonies" , "style of music" .)