Trainee put in ground nuts, at first (6)
I believe the answer is:
intern
'trainee' is the definition.
(intern can mean a trainee worker)
'put in ground nuts at first' is the wordplay.
'put in ground' becomes 'inter' (I've seen this before).
'at first' indicates taking the first letters.
The initial letter of 'nuts' is 'n'.
'inter'+'n'='INTERN'
(Other definitions for intern that I've seen before include "Often unpaid trainee" , "to keep under lock and key" , "Official language of Pakistan" , "22 [IMPRISON]" , "Medical graduate trainee" .)