the doctrine that an individual state of the U.S. may oppose any federal action it believes encroaches on its sovereignty.
Origin: 1375–1425; late Middle English interposicio(u)n < Latin interpositiōn- (stem of interpositiō), equivalent to interposit(us) (past participle of interpōnere to place between) + -iōn--ion
early 15c., from O.Fr. interposicion (12c.), from L. interpositionem (nom. interpositio), from interpositus, pp. of L. interponere, from inter- + ponere (see position).