Constricted or warned off (8)
I believe the answer is:
narrowed
'constricted' is the definition.
('narrow' can be a synonym of 'constrict')
'or warned off' is the wordplay.
'off' indicates an anagram.
'or'+'warned'='orwarned'
'orwarned' anagrammed gives 'NARROWED'.
(Other definitions for narrowed that I've seen before include "Shrank from" , "Grew less wide" , "grew closer" , "Reduced in width" , "Tapered" .)