Fool, English, stops device working (7)
I believe the answer is:
deceive
'fool' is the definition.
(I've seen this in another clue)
'english stops device working' is the wordplay.
'english' becomes 'e' (abbreviation).
'stops' indicates putting letters inside.
'working' indicates an anagram.
'device' with letters rearranged gives 'decive'.
'e' put into 'decive' is 'DECEIVE'.
(Other definitions for deceive that I've seen before include "Cheat or mislead" , "Mislead, delude" , "Intentionally mislead" , "Deliberately mislead" , "Delude or betray" .)