Facility is seen as strange (8)
I believe the answer is:
easiness
'facility' is the definition.
(thesaurus)
'is seen as strange' is the wordplay.
'strange' indicates an anagram.
'is'+'seen'+'as'='isseenas'
'isseenas' with letters rearranged gives 'EASINESS'.
(Other definitions for easiness that I've seen before include "Nonchalance" , "Facile quality" , "Lack of difficulty" .)