Clears off after six being instinctive (8)
I believe the answer is:
visceral
'instinctive' is the definition.
(I've seen this before)
'clears off after six' is the wordplay.
'off' is an anagram indicator.
'after' means one lot of letters go next to another.
'six' becomes 'vi' (roman numeral).
'clears' anagrammed gives 'sceral'.
'sceral' put after 'vi' is 'VISCERAL'.
'being' is the link.
(Other definitions for visceral that I've seen before include "Relating to internal organs of the body" , "Relating to deep inner feelings" , "Relating to deep feelings - claviers (anag)" , "Relating to organs (or instincts) - claviers (anag)" , "Intuitive rather than cerebral" .)