The language we call Old English was spoken in England from some time in the fifth century through the eleventh century. Students just beginning to learn Old English are often struck by both the similarities and the differences between Old English and the Modern English we speak today. Despite variations in spelling, many words still bear much the same meanings now as they did then. Others, however, have changed greatly in their meanings, either narrowing their range of meaning or expanding and eventually shifting their meanings.
Let's look first at examples of words that have narrowed in their meanings. The Old English word dōm has evolved into our Modern English doom. We think of doom as something negative, a judgment that sends a person to some horrible fate. The Old English dōm could mean that, too, but not always. It also refers to simply a ruling or decision that might be either positive or negative, but it can also refer to glory, honor, praise, and majesty, all definitions we would never associate with doom today.
A similar narrowing has occurred with the verb sellan. When we think about selling something today, we think about exchanging money for some object or service. The Old English verb can mean that, too, but it also carries a broader definition, simply to give something to someone, a physical object, perhaps, or a service, a reward or punishment, or even something abstract like forgiveness. We would never think of using our Modern English verb sell to express any of those concepts, but the Old English sellan worked perfectly well.
For another example, consider the word cwēn. It looks a little strange, but it is actually the Old English spelling of the modern queen. It did not, however, only refer to the wife of a king as it does today. It could actually be used to identify any woman no matter what her social status. The word could also mean simply wife.
While these words, and many others, narrowed their meanings over time, other words expanded their meanings to include new definitions, then dropped their older references, leading to a significant shift in meaning between their Old English and Modern English forms. What does the modern noun spell suggest? Most of us probably think of magic spells, words spoken to perform some spectacular and mysterious feat, but the Old English spell did not mean that at all. An Old English spell is usually a story or sometimes an informative talk, like a sermon or even a message or announcement. Only over time did the word come to refer to a spell as we think of it today, and gradually older meanings dropped away, leaving only the new meaning in place.
The Old English word gesǣlig probably does not look too familiar, but it is the ancestor of the modern silly. Gesǣlig, however, means happy, blessed, or prosperous rather than foolish or goofy. Those meanings developed over time and came to dominate the word so that older, more positive meanings faded away, leaving only the silly we have today.
We can try one more example, the Old English mōd, which means the innermost part of a person— one's mind, heart, or soul. That is quite different from the modern mood, which refers to one's state of mind or feelings at a particular time. Again, the meaning of mōd expanded over time to include the subjective state of mind as well as the mind itself, and eventually the original meaning dropped off, leaving the one we have today.
The meanings of some Old English words, then, either narrowed over time to include only one aspect of the original definition or expanded to take on new meanings, often leaving old ones behind as the years passed and English changed into its modern form.