John’s English, imprecise (5)
I believe the answer is:
loose
'imprecise' is the definition.
('loose' can be similar in meaning to 'imprecise')
'john's english' is the wordplay.
'john's' becomes 'loos' (loo is a kind of john).
'english' becomes 'e' (abbreviation).
'loos'+'e'='LOOSE'
(Other definitions for loose that I've seen before include "Unleash" , "Not crammed" , "Water heater" , "Not fitting tightly" , "Not tight" .)