/ˈɑːptɪməm/
op·ti·mum
BrE /ˈɒptɪməm/
NAmE /ˈɑːptɪməm/
[only before noun]
(also op·ti·mal)
the best possible; producing the best possible results
optimum growth
the optimum use of resources
the optimum conditions for effective learning
the optimum [sing.]
the best possible result, set of conditions, etc.
SYN ideal