Very best, most favourable (7)
I believe the answer is:
optimum
I believe this is a double definition.
'very best' is the first definition.
(I've seen this before)
'most favourable' is the second definition.
(I've seen this before)
(Other definitions for optimum that I've seen before include "Best, most favourable" , "top condition" , "Most appropriate" , "Most favourable amount" , "Most favourable point" .)