Perhaps this can help as well:
The Catechism of the Council of Trent, Part II, Chapter IV
QUESTION III
Why this Sacrament is called Eucharist
Wherefore the sacred writers, seeing that it was not at all possible that they should demonstrate by one term the dignity and excellence of this admirable sacrament, endeavoured to express it by many words. For sometimes they call it Eucharist; which word we may render in Latin either good grace, or giving of thanks. And rightly, indeed, is it to be called good grace, as well because it first signifies eternal life, concerning which it has been written: the grace of God is eternal life; and also because it includes in it Christ the Lord, who is true grace and the fountain of all favours. And no less aptly do we interpret it a giving of thanks; inasmuch as, when we immolate this purest victim, we give daily unbounded thanks to God for all his kindnesses towards us, and above all for so excellent a gift of his grace, which he assigns to us in this sacrament. But that very name, also, agrees best with those things which we read were done by Christ the Lord, at the institution of this mystery. For taking bread he brake it, and gave thanks. David also, when he would contemplate the greatness of this mystery, before he pronounced that verse: He hath made his wonderful works to be remembered; the Lord is gracious, and full of compassion. He hath given meat unto them that fear him, thought that the giving of thanks should be placed first, when he says: confession and magnificence are his work.
QUESTION XL
This Wondrous Conversion is appropriately called Transubstantiation
This admirable conversion then, as the Sacred Council of Trent has taught, is accurately and appropriately called by the holy Catholic Church Transubstantiation, for as natural generation, because in it the form [of existence] is changed, may properly and appropriately be called transformation; so, in like manner, to express the change that takes place in the sacrament of the Eucharist, in which the whole substance of one thing passes into the whole substance of another, the word Transubstantiation was rightly and wisely introduced by our predecessors in the faith.
QUESTION XLI
The Manner of Transubstantiation, and the Place in which Christ is in this Sacrament, must not be curiously searched into
But in accordance with the principle so often repeated by the Fathers, the faithful are to be admonished that they do not inquire too curiously into the manner in which this change may be made, for it defies our powers of conception, nor have we any example of it in natural changes, nor in the creation of things itself. The change itself is to be learnt by faith; the manner thereof is not to be made a subject of too curious inquiry. Pastors should also use no less caution in explaining the mysterious manner, in which the body of our Lord is contained whole and entire under the least particle of the bread: such disputations will scarcely ever have to be entered upon; should, however, Christian charity require it, the pastor will recollect previously to fortify the minds of the faithful, by reminding them that no thing shall be impossible with God.
Peace,
