most favorable conditions or greatest degree or amount possible under given circumstances
"The garden yields the best harvest when planted during the optimum season of spring and early summer."
The best or most favorable condition, or the greatest amount or degree possible under specific sets of comparable circumstances.
"The garden produces the highest yield when kept at its optimum temperature and moisture levels."
In plain English: Optimum is the perfect amount of something that makes everything work as well as it possibly can.
"The optimum temperature for baking this cake is 350 degrees Fahrenheit."
Usage: Use this noun to describe a peak level that cannot be exceeded without diminishing returns, such as an optimum temperature for plant growth. It is often confused with "optimal," which functions only as an adjective describing the ideal state itself rather than measuring its degree.
The best or most advantageous; surpassing all others.
"The sunlight streaming through the skylight provided the optimum conditions for growing rare orchids in our small apartment."
In plain English: Optimum means being as good, effective, or perfect as possible for a specific situation.
"The optimum temperature for growing tomatoes is between seventy and eighty degrees Fahrenheit."
Optimum comes from New Latin, where it was originally an adjective meaning "the best" derived from the Latin word optimus. The term entered English with this same sense of being optimal or most favorable.