Wrongly see nudism as trend to reform (13)
I believe the answer is:
misunderstand
'wrongly see' is the definition.
(to misunderstand is to see something incorrectly)
'nudism as trend to reform' is the wordplay.
'to reform' is an anagram indicator.
'nudism'+'as'+'trend'='nudismastrend'
'nudismastrend' anagrammed gives 'MISUNDERSTAND'.
(Other definitions for misunderstand that I've seen before include "Take wrongly" , "Fail to see" , "Fail to interpret correctly" , "Fail to follow" , "Get wrong idea of" .)