The word tide, which we now apply to the regular rise and fall of the sea, used to mean in Old English "time;" and it still keeps this meaning in the words Christmastide, Whitsuntide, etc.
One common way in which words change is in going from a general to a more special meaning. Thus in Old English the word chest meant "box" in general, but has come now to be used as the name of a special kind of box only, and also as the name of a part of the body. The first person who used the word in this sense must have thought of the "chest" as a box containing the lungs and the heart.
Glass is, of course, the name of the substance out of which we make our windows and some of our drinking vessels, etc., and this was at one time its only use; but we now use the name glass for several special articles—for example, a drinking-vessel, a telescope, a barometer, a mirror (or "looking-glass"), and so on. Copper is another word the meaning of which has become specialized in this way as time has gone on. From being merely the name of a metal it has come to be used for a copper coin and for a large cauldron especially used in laundry work. Another example of a rather different kind of this "specialization" which changes the meaning of words is the word congregation. Congregation used to mean "any gathering together of people in one place," and we still use the word congregate in this sense. Thus we might say "the people congregated in Trafalgar Square," but we should never think of speaking of a crowd listening to a lecturer there as a "congregation." The word has now come to mean an assembly for religious worship in a chapel or church.
Some words have changed their meaning in just the opposite way. From having one special meaning they have come by degrees to have a much more general sense. The word bureau, which came into English from the French, meant at first merely a "desk" in both languages. It still has this meaning in both languages, but a wider meaning as well. It can now be used to describe an office (a place associated with the idea of desks). Thus we have "employment bureau," and can get English money for foreign at a "bureau de change." From this use of the word we have the word bureaucracy, by which we describe a government which is carried on by a great number of officials.
A better example of how a word containing one special idea can extend its meaning is the word bend. This word originally meant to pull the string of a bow in order to let fly an arrow. The expression "bend a bow" was used, and as the result of pulling the string was to curve the wooden part of the arrow, people came in time to think that "bending the bow" was this making the wood to curve. From this came our general use of "bend" to mean forcing a thing which is straight into a curve or angle. We have, of course, also the metaphorical use of the word, as when we speak of bending our will to another's.
Another word which has had a similar history is carry. When this word was first borrowed from Old French it meant to move something from place to place in a cart or other wheeled vehicle. The general word for our modern carry was bear, which we still use, but chiefly in poetry. In time carry came to have its modern general sense of lifting a thing from one place and removing it to another. A well-known writer on the history of the English language has suggested that this came about first through people using the word in this sense half in fun, just as the word cart is now sometimes used. A person may say (a little vulgarly), "Do you expect me to cart all these things to another room?" instead of using the ordinary word carry. If history were to repeat itself in this case, cart might in time become the generally used word, and carry in its turn be relegated to the realm of poetry.
Words often come to have several meanings through being used to describe things which are connected in some way with the things for which they were originally used. The word house originally had one meaning, which it still keeps, but to which several others have been added. It was a building merely, but came in time to be used to mean the building and the people living in it. Thus we say one person "disturbs the whole house." From this sense it got the meaning of a royal family, and we speak of the House of York, Lancaster, Tudor, or Stuart. We also use the word in a large sense when we speak of the "House of Lords" and the "House of Commons," by which we hardly ever mean the actual buildings known generally as the "Houses of Parliament," but the members of the two Houses. The word world has had almost the opposite history to the word house. World originally applied only to persons and not to any place. It meant a "generation of men," and then came to mean men and the earth they live on, and then the earth itself; until it has a quite general sense, as when we speak of "other worlds than ours."
Many words which are used at present to describe bad or disagreeable things were used quite differently originally. The word villain is, perhaps, the most expressive we can use to show our opinion of the depths of a person's wickedness. Yet in the Middle Ages a villain, or "villein," was merely a serf or labourer bound to work on the land of a particular lord. The word in Saxon times would have been churl. As time went on both these words became terms of contempt. The lords in the Middle Ages were certainly often more wicked than the serfs, as we see in the stories of the days of Robin Hood; but by degrees the people of the higher classes began to use the word villain more and more contemptuously. Many of them imagined that only people of their own class were capable of high thoughts and noble conduct. Gradually "villainy" came to mean all that was low and vulgar, and by degrees it came to have the meaning it has now of "sheer wickedness." At the end of the Middle Ages there were practically no longer any serfs in England; but the word villain has remained in this new sense, and gives us a complete story of the misunderstanding and dislike which must have existed between "noble" and "simple" to cause such a change in the meaning of the word.
The word churl has a somewhat similar history. We say now that a sulky, ungracious person is a "mere churl," or behaves in a "churlish" manner, never thinking of the original meaning of the word. Here, again, is a little story of injustice. The present use of the word comes from the supposition that only the mere labourer could behave in a sulky or bad-tempered way.
Knave is another of those words which originally described persons of poor condition and have now come to mean a wicked or deceitful person. A knave, as we now understand the word, means a person who cheats in a particularly mean way, but formerly the word meant merely "boy." It then came to mean "servant," just as the word garçon ("boy") is used for all waiters in French restaurants. Another word which now means, as a rule, some one unutterably wicked, is wretch, though it is also used rather contemptuously to describe some one who is not wicked but unutterably miserable. Yet in Old English this word merely meant an "exile." An exile was a person to be pitied, and also sometimes a person who had done something wrong, and we get both these ideas in the modern uses of the word. The word blackguard, which now means a "scoundrel," was also once a word for "scullion;" but it does not go back as far as "knave" and "villain," being found chiefly in writings of the sixteenth and seventeenth centuries.