A hint that's neither across nor down (6)
I believe the answer is:
ascent
'neither across nor down' is the definition.
(climbing up so not down or across)
'a hint' is the wordplay.
'hint' becomes 'scent' (I've seen this in another clue).
'a'+'scent'='ASCENT'
'that's' acts as a link.
(Other definitions for ascent that I've seen before include "Stance (anag)" , "Upward climb" , "Upward slope" , "Act of moving upwards" , "A climb or way up" .)