Intern beginning to cotton on all right (7)
I believe the answer is:
confine
'intern' is the definition.
(thesaurus)
'beginning to cotton on all right' is the wordplay.
'beginning to' says to take the initial letters.
'all right' becomes 'fine' ('fine' can be a synonym of 'all right').
The first letter of 'cotton' is 'c'.
'c'+'on'+'fine'='CONFINE'
(Other definitions for confine that I've seen before include "Limit" , "Keep within limits" , "pen" , "Imprison" , "Incarcerate" .)