Nothing is as strange or surprising (11)
I believe the answer is:
astonishing
'surprising' is the definition.
(similar in meaning)
'nothing is as strange' is the wordplay.
'strange' indicates anagramming the letters.
'nothing'+'is'+'as'='nothingisas'
'nothingisas' anagrammed gives 'ASTONISHING'.
'or' is the link.
(Other definitions for astonishing that I've seen before include "Greatly surprising" , "impressive" , "Amazing" , "Mind-boggling" .)