Q. 1. What is the Catholic definition of the word "transubstantiation?"
A. 1. In the Holy Bible we read;
"Then he took a loaf of bread, and when he had given thanks, he broke it and gave it to them, saying, 'This is my body, which is given for you. Do this in remembrance of me.'" [Lk. 22:19]
Roman Catholics literally take Jesus at His word: the bread is His Body; the wine is His Blood. To the revealed Word that "my flesh is true food, my blood is true drink" the Church labeled this belief as "Transubstantiation."
From the early days of the Church at the Last Supper until today, the bread and wine of the Eucharist look and feel and taste like bread and wine in the eating and drinking of them. The acceptance of "transubstantiation" is a matter of faith. Even though the bread does not look, feel, taste like flesh; even though the wine does not look, feel, taste like blood, they are the Body and Blood of Christ.
Faith means being sure of the things that we hope for and knowing that something is real even if we do not see it. If we can believe that electricity is real, heat and cold are real, the wind moves, than we can believe what Jesus said.