Q: Why do we say “twenty-four,” “thirty-four,” “forty-four,” etc., but we don’t say “onety-four” for “fourteen”?
A: The suffix “-ty” here denotes multiples of ten, so “twenty-four” would be two tens plus four, “thirty-four” would be three tens plus four, and so on.
The “-ty” suffix is used for multiples of two to nine tens. When only one ten is involved, it’s represented by the suffix “-teen.” So “fourteen” would be four plus ten, “fifteen” would be five plus ten, and so on.
This system dates back to Old English, the language of the Anglo-Saxons, where “-ty” was tig, “twenty” was twentig, and “thirty” was þrítig. In Old English writing, “-teen” was –téne, -tīene, etc., “fourteen” was féowerténe, and “fifteen” was fífténe, according to the Oxford English Dictionary.
You may be wondering why “eleven” isn’t “oneteen” and “twelve” isn’t “twoteen” in Modern English. This usage also dates back to Old English, where “eleven” was endleofan, and “twelve” was twelf.
Although there’s some doubt about the ultimate origin of “eleven” and “twelve,” The American Heritage Dictionary of Indo-European Roots says the usage comes from prehistoric Germanic: “eleven” from ain-lif (“one left” beyond ten) and “twelve” from twa-lif (“two left” beyond ten).
Finally, we should mention that English has another “-ty” suffix, one used to form nouns denoting a quality or condition, such as “ability,” “certainty,” “modesty,” and “responsibility.” These nouns ultimately come from Latin, though many arrived in English by way of French.
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