Occasionally good to query smell (5)
I believe the answer is:
odour
'smell' is the definition.
(I know that smell can be written as odour)
'occasionally good to query' is the wordplay.
'occasionally' indicates alternate letters.
'good'+'to'+'query'='goodtoquery'
The alternating letters of 'goodtoquery' are 'ODOUR'.
(Other definitions for odour that I've seen before include "Small, aroma" , "Smell, redolence" , "essence" , "Aroma or fragrance" , "Stink" .)