Charity, caritas, occupies two places at once, and the overlap is worth stating clearly. In the popular scheme of contrary virtues it stands against avarice, and there it means generosity, the free giving of what one has; the older term for that is liberalitas, and some presentations of the scheme use it. In the theological scheme, however, charity is the third and greatest of the theological virtues named by Paul at 1 Corinthians 13, and there it means the love of God and of one's neighbour for God's sake, which Aquinas calls the form of all the virtues, the principle that gives them their order and without which they are not, properly speaking, virtues at all. The Greek behind it is agape, the Latin caritas, and the English translation has drifted so far toward almsgiving that most modern versions render it love.
The word's drift in English reflects a specific translation history: William Tyndale's earlier English New Testament rendered the term at 1 Corinthians 13 simply as love, but the translators of the 1611 King James Version reverted to charity, following the Latin Vulgate's caritas, a choice that shaped English religious vocabulary for centuries even as it narrowed the word's later everyday sense toward almsgiving specifically. C. S. Lewis's twentieth-century study The Four Loves revisited the underlying Greek vocabulary, agape, eros, philia, and storge, for a popular readership, distinguishing agape as a love given without regard to the worth or attractiveness of its object, the sense the theological virtue of charity is meant to carry.