/ob verr"zheuhn, -sheuhn/ , n.
1. an act or instance of obverting.
2. something that is obverted.
3. Logic. a form of inference in which a negative proposition is obtained from an affirmative, or vice versa, as "None of us is immortal" is obtained by obversion from "All of us are mortal."
[ 1840-50; obversion- (s. of obversio ) a turning toward, equiv. to obvers ( us ) (see OBVERSE) + -ion- -ION ]