1. the Roman Catholic doctrine that the whole substance of the bread and the wine changes into the substance of the body and blood of Christ when consecrated in the Eucharist • Derivationally related forms: transubstantiate • Hypernyms: theological doctrine 2. an act that changes the form or character or substance of something • Syn: transmutation • Derivationally related forms: transubstantiate, transmute (for: transmutation) • Hypernyms: conversion