Pronunciation: (op'tu-mum), [key]
—n., pl. -maPronunciation: (-mu), [key] -mums,
1. the best or most favorable point, degree, amount, etc., as of temperature, light, and moisture for the growth or reproduction of an organism.
2. the greatest degree or best result obtained or obtainable under specific conditions.
most favorable or desirable; best: optimum conditions.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.