Arsenic classified as 'miscellaneous' (8)
I believe the answer is:
assorted
'miscellaneous' is the definition.
(synonyms)
'arsenic classified' is the wordplay.
'arsenic' becomes 'as' (As is the chemical symbol for arsenic).
'classified' becomes 'sorted' ('sort' can be a synonym of 'classify').
'as'+'sorted'='ASSORTED'
'as' is the link.
(Other definitions for assorted that I've seen before include "Containing various different kinds" , "Miscellaneous, sundry" , "Manifold" , "Various, diverse" , "Mixed" .)