You use maximum to describe an amount which is the largest that is possible, allowed, or required. Maximum definition: An upper limit permitted by law or other authority. MAXIMUM definition: 1. being the largest amount or number allowed or possible: 2. the largest amount allowed or…. Learn more. MAXIMUM definition: the greatest quantity or amount possible, assignable, allowable, etc. See examples of maximum used in a sentence. Definition of maximum noun in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. Both a noun and an adjective, maximum takes it to the max: it means the most, the fastest, the biggest. The meaning of MAXIMUM is the greatest quantity or value attainable or attained. If you say that something is a particular amount maximum, you mean that this is the greatest amount it should be or could possibly be, although a smaller amount is acceptable or very possible. In mathematical analysis, the maximum and minimum[a] of a function are, respectively, the greatest and least value taken by the function. MAXIMUM meaning: 1. being the largest amount or number allowed or possible: 2. the largest amount allowed or…. Learn more.