OPTIMUM

optimum, optimal

(adjective) most desirable possible under a restriction expressed or implied; “an optimum return on capital”; “optimal concentration of a drug”

optimum

(noun) most favorable conditions or greatest degree or amount possible under given circumstances

Source: WordNet® 3.1

Etymology

Noun

optimum (plural optima or optimums)

The best or most favorable condition, or the greatest amount or degree possible under specific sets of comparable circumstances.

Adjective

optimum (not comparable)

The best or most advantageous; surpassing all others.

Synonyms: best, ideal, optimal

Source: Wiktionary