Is there a term in (English) linguistics for a word that belongs to more than one word class?

For example fast, which can be either an adjective, or a noun.

I've been trying to find a term for this, and the closest I've come up with is conversion or zero derivation. (source)

My doubt is that this seems to describe a process of word formation in new categories, whereas I'm looking to describe the quality of belonging to more than one category.

Is that the one?

Many thanks.

  • 3
    No, there's no established term, though I suppose we could talk of "multi-category" for those lexemes that belong to two or more categories. Btw, "fast" can also be an adverb, as in "Ed was driving too fast". – BillJ Mar 8 at 11:48
  • Thank you. I've kept looking, and so far the best I've found is "part-of-speech flexibility". I'll just stick with a descriptive turn of phrase, then. – Matt S. Mar 8 at 11:50
  • 1
    That's a bit of a mouthful! One of my grammar books talks of 'overlap between the categories', but that's just another way of expressing your point. – BillJ Mar 8 at 11:57
  • 1
    I don't know if it is used this way formally, but 'polysemy', meaning 'having many different meanings', could be applied in this instance, since a change in POS involves a change in meaning (even if the meaning is mostly otherwise the same). Can anybody who actually knows confirm/deny? – Mitch Mar 13 at 19:15
  • Having had a cursory look, it would seem that the example I gave would indeed be of homonymy--but I'm beginning to suspect what I'm looking for is actually closer to your suggestion, so I'll bear that in mind, with thanks. – Matt S. Mar 13 at 19:31

In general, these are called homonyms, especially in cases like fast (period of not eating) vs fast (moving quickly), where neither is derived from the other. In cases like these, they seem to be stored as separate lexemes in the brain, and it's just coincidence that they look the same. This can even happen when the words are related, if they've diverged enough: even though fast (moving quickly) comes from fast (securely, as in "stuck fast"), modern English-speakers see them as separate words.

Zero derivation (and derivation in general) usually refers to a different process, where there's only one underlying lexeme in your mental model of the language, and the part of speech is determined by how you use it (or what you attach to it). For example, if I say "the new light bulbs really greenified the whole room", you don't have a mental lexeme for "greenify" (especially since I just made it up)—instead, you have lexemes for "green" and "-ify" that you stick together to get the meaning.

  • This is very helpful. Based on this, I found some useful tables on Wikipedia (en.m.wikipedia.org/wiki/Homonym#Related_terms), listing the different terms in different cases. I'm looking for an English term, but the source language is Classical Chinese, which brings with it some added complications. "二" means "two", as an ordinal or cardinal number, but I could write "二其言" ("to 'two' his words"), meaning "to prevaricate", or perhaps "be hypocritical". The 二 is pronounced the same, so I'm confident in calling this verbification, and an example of a homonymy. – Matt S. Mar 8 at 16:44
  • Depending on the specific case, I'll be able to go with the related terms "homophone" and "homograph", too. Thanks again. – Matt S. Mar 8 at 16:45
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    I think @Draconis is right. I've studied some cases of homonyms like Dubinsky & Semango (1996), Haspelmath (1987), Siewierska (1979), among others, and I've arrived at distinguishing between 'random or accidental' homonymy and 'systematic' homonymy. I think Matt S. is referring to the first type, if yes, then they can be called 'homonymy', but if the pair in question has systematic homonymy (as in systematic voice syncretism), then the word won't be accurate. – Tsutsu T. Mar 8 at 17:04

To my knowledge, if the category varies according to the syntactic context projected in, i.e. an adjective in X & a noun in Y, there won't be a stable or fixed categoy status that would label it. Other technical words like the one you've mentioned can be used (but again it's a question of context). If the functional projection DP hosts 'fast', it's realizied as its complement NP corresponding to a noun, but if ADJP projection hosts it, it's realized as an adjective.

  • I'm sorry, linguistics isn't my field (hence my question), so the above is incomprehensible to me, especially the last sentence. I assume "DP" is "determiner phrase", by proximity with "NP" and "ADJP", but I don't know what you mean by "realized" or "functional projection". – Matt S. Mar 8 at 16:14
  • 1
    I'm sorry for the poor choice of words, you can read my last comment on @Draconis answer. – Tsutsu T. Mar 8 at 17:05

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