Enter, still without son (6)
I believe the answer is:
insert
'enter' is the definition.
('insert' can be a synonym of 'enter')
'still without son' is the wordplay.
I cannot quite understand how this works, but
'son' could be 's' and 's' is found in the answer.
'still' could be 'inert' (I've seen this before) and 'inert' is found in the leftover letters.
No letters remain.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for insert that I've seen before include "place in the interior" , "Place (something) inside (something else)" , "Place within, pages of a publication say" , "Enter" , "Introduce, put in" .)