I just discovered this one a short time ago while working on an article about language. Here’s the definition based on the Wikipedia entry:

Polysemy: the capacity for a sign, word, or phrase to have multiple related meanings. It is usually regarded as distinct from homonymy, in which the multiple meanings of a word may be unconnected or unrelated.

For example, a word like man would qualify as being polysemous because the meanings are related. Let’s look at them:

• Man: humankind (both male and female, old and young)
• Man: specifically a male human being
• Man: even more specifically an adult male human being

Those are very obviously related as they all refer to human beings.

Wikipedia includes another one that I think is even better:

• Book: a bound collection of pages (could be a blank book)
• Book: a reproduced and distributed text (not a blank book, and perhaps not even paper pages (a digital book, for example)
• Book: a verb meaning to record or make an entry in a ledger (a book!) or today in a computer file.

It seems rather common in language to find nouns become verbs and vice versa.

This would be opposed to a homonym like the word stalk:

• Stalk: the stem of a plant
• Stalk: verb meaning to follow and harass either an animal or person

There is some debate, it seems about whether polysemy is a distinct category or a subset of homonymy. It seems to me, though, that a great many homonyms are actually words that came to have a new meaning through metaphor.

Like the the mouth of an animal and the mouth of a river, for example.

Also in Wikipedia’s list of homonyms there are words like:

• Change: verb meaning to become something different
• Change: noun meaning money converted into a collection of different denominations
• Change: noun meaning the difference between an amount of money charged for an item and the amount given to pay

The above are clearly related definitions.

Anyway, a very interesting word and one that I think is useful.

Polysemy, of course, if not properly recognized, can lead to the fallacy of equivocation.