/in'teuhr peuh zish"euhn/ , n.
1. the act or fact of interposing or the condition of being interposed.
2. something interposed.
3. the doctrine that an individual state of the U.S. may oppose any federal action it believes encroaches on its sovereignty.
[ 1375-1425; late ME interposicio ( u ) n interposition- (s. of interpositio ), equiv. to interposit ( us ) (ptp. of interponere to place between) + -ion- -ION ]