To be audacious is unknown in Greek god (3,2,2)
I believe the answer is:
try it on
'to be audacious' is the definition.
(I've seen this before)
'unknown in greek god' is the wordplay.
'unknown' becomes 'y' (algebra).
'in' indicates putting letters inside.
'greek god' becomes 'triton' (Triton is an example**).
'y' going within 'triton' is 'TRY IT ON'.
'is' is the link.
(Other definitions for try it on that I've seen before include "Attempt to be provocative (colloq.)" , "Be cheeky" , "Before buying a dress, you should" , "Attempt to deceive" , "be bold" .)