Asian trio hard at it, originally (4)
I believe the answer is:
thai
'asian' is the definition.
(I know that Thai is a type of asian)
'trio hard at it originally' is the wordplay.
'originally' says to take the initial letters.
The initial letters of 'trio hard at it' is 'THAI'.
(Other definitions for thai that I've seen before include "Morte d'16author" , "Sort of eastern cooking" , "Person from Bangkok?" , "Asian tongue" , "Someone from Bangkok, perhaps" .)