Stop colonial worker crossing North America (9)
I believe the answer is:
terminate
'stop' is the definition.
('terminate' can be a synonym of 'stop')
'colonial worker crossing north america' is the wordplay.
'colonial worker' becomes 'termite' (termites work in colonies).
'crossing' is an insertion indicator.
'north america' becomes 'na'.
'termite' placed around 'na' is 'TERMINATE'.
(Other definitions for terminate that I've seen before include "Close" , "Put an end to, finish" , "Finalise" , "Put an end to, discontinue" , "Bring to an end" .)