The Oxford Thesaurus An A-Z Dictionary of Synonyms - optimum n.

1) best, finest, most favourable, ideal, perfection, model, paragon, exemplar: In all work, the optimum is difficult to achieve. --adj. 2) best, finest, most favourable, ideal, perfect, choicest, optimal, first-rate, first-class, sterling, prime, capital, excellent, exceptional, superlative, extraordinary, unique, peerless, unequalled, unexcelled, unsurpassed: These instruments keep the chamber at the optimum temperature. After months of training, Guy is in optimum condition to win the marathon.