Boss overseeing ten in workshop (6)
I believe the answer is:
studio
'workshop' is the definition.
(I've seen this before)
'boss overseeing ten' is the wordplay.
'boss' becomes 'stud' (synonyms).
'overseeing' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'ten' becomes 'io' (IO resembles 10).
'stud'+'io'='STUDIO'
'in' acts as a link.
(Other definitions for studio that I've seen before include "Workplace for the practice of art" , "Recording room" , "Artist's workroom - film company" , "Where an artist works" , "Artist's workshop" .)