Boreal hornet turned up near ... (8)
I believe the answer is:
northern
'boreal' is the definition.
(similar in meaning)
'hornet turned up near' is the wordplay.
'turned' is an anagram indicator.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'near' becomes 'nr' (abbreviation used in addresses).
'nr' reversed gives 'rn'.
'hornet' with letters rearranged gives 'northe'.
'northe'+'rn'='NORTHERN'
(Other definitions for northern that I've seen before include "14 13" , "'... lights, Aurora Borealis (8)'" , "in Scotland?" , "Relating to Antrim, say" , "Relating to Belfast, say" .)