Hosing stain off is surprising (11)
I believe the answer is:
astonishing
'is surprising' is the definition.
(similar in meaning)
'hosing stain off' is the wordplay.
'off' indicates anagramming the letters.
'hosing'+'stain'='hosingstain'
'hosingstain' is an anagram of 'ASTONISHING'.
(Other definitions for astonishing that I've seen before include "Mind-boggling" , "Amazing" , "impressive" , "Greatly surprising" .)