Get hold of the painter in "Great Britain" (4)
I believe the answer is:
grab
'get hold of' is the definition.
(thesaurus)
'the painter in great britain' is the wordplay.
'the painter' becomes 'ra'.
'in' means one lot of letters goes inside another.
'great britain' becomes 'gb'.
'ra' going within 'gb' is 'GRAB'.
(Other definitions for grab that I've seen before include "Take quickly" , "Impress" , "'Seize, snatch (4)'" , "Seize suddenly" , "Grasp roughly" .)