I. (ˌ)in-ˈvərs, ˈin-ˌ adjective
Etymology: Middle English, turned upside down, from Latin inversus, from past participle of invertere
Date: 15th century
1. : opposite in order, nature, or effect
2. : being an inverse function
inverse sine
II. noun
Date: circa 1681
1. : something of a contrary nature or quality : opposite , reverse
2. : a proposition or theorem formed by contradicting both the subject and predicate or both the hypothesis and conclusion of a given proposition or theorem
the inverse of “if A then B” is “if not-A then not-B”
— compare contrapositive
3.
a. : inverse function ; also : an operation (as subtraction) that undoes the effect of another operation
b. : a set element that is related to another element in such a way that the result of applying a given binary operation to them is an identity element of the set