In this matter the English language is very different from the German. The English language has many words which the Germans have too, but their meanings are different. The Germans have kept the original meanings which these words had hundreds of years ago; but the thousands of words which have come down to us from the English language of a thousand years ago have nearly all changed their meanings.
We have two of these old words which have now each two exactly opposite meanings. The word _fast_ means sometimes "immovable," and sometimes it means the exact opposite--"moving rapidly." We say a key is "fast" in a lock when we cannot get it out, and we say a person runs "fast" when we mean that he runs quickly. The first meaning of steadiness is the original meaning; then the word came to be used to mean "moving steadily." A person who ran on, keeping up a steady movement, was said to run fast, and then it was easy to use the word for rapidity as well as steadiness in motion or position. This is how the word _fast_ came to have two opposite meanings.
Another word, _fine_, has the same sort of history. We speak of a "fine needle" when we mean that it is thin, and a "fine baby" when we mean that it is fat. The first meaning is nearer to the original, which was "well finished off." Often a thing which had a great deal of "fine" workmanship spent on it would be delicate and "fine" in the first sense, and so the word came to have this meaning. On the other hand, the thing finished off in this way would generally be beautiful. People came to think of "fine" things as things to be admired, and as they like their babies to be fat, a fat baby will generally be considered a fine baby. It was in this kind of way that "fine" came to have its second meaning of "large."
The common adjectives _glad_ and _sad_ had quite different meanings in Old English from those they have now. In Old English glad meant "shining," or "bright," but in a very short time it came to mean "cheerful." Now it means something rather different from this, for though we may speak of a "glad heart" or "glad spirit," such expressions are chiefly used in poetry. Generally in ordinary speech when we say that we are "glad" we mean that we are pleased about some special thing, as "glad that you have come."