§125. Latin Number Words in English

You will observe that there are a few English number words that closely reflect original Latin number words. These include duo, cent (along with percent); prime, second, quart; and single. Modern month names, from September to December, are adapted without change from their Latin counterparts—though there seems to be something wrong with the arithmetic of the Roman calendar.^[1]

In general, however, Latin number vocabulary has entered the English language as COMBINING FORMS, which—in the Latin language itself—were sometimes quite different from the independent number words. The Latin cardinal number “four,” for instance—quattuor—is of no relevance to English; but the Latin combining form quadr- has been very useful. Similarly, the Latin word “two” (duo) is far less essential to English than the form bi-. Therefore the numerical vocabulary of §124 consists mainly of combining forms, as you may infer from the hyphens following most items. Remember that Latin generally uses the connecting vowel -i- to link a combining form with another word base (see Part I, §92; for example, un-i-verse, cent-i-pede). That standard principle will usually apply, though there are some exceptions—primo-geniture (an adverbial first element) and quadr-u-ped (the archaic connecting vowel -u- was sometimes used with quadr-).

The best way to see these principles at work may be to look at several parallel English words that use Latin combining forms for “one” and “two” (un- and bi-):

As these examples suggest, numerical prefixes often draw our attention to contrasts; unilateral decisions may be opposed to those that are bilateral or multilateral. (Although Latin mult– and Greek poly- [πολυ-] are not, strictly speaking, number words, they play an obvious role in compounds of this type.) A biped may be contrasted with a quadruped or a multiped—not to mention a centipede or a millipede. In the muscle names biceps, triceps (upper arm), and quadriceps (thigh), the -ceps element is derived from L caput (“head”). Numerical compounds are conspicuous in geometry, of course: triangle and quadrangle derive from L angulus (“corner,” “angle”).^[4]

We could list many more English words containing the Latin combining form bi-: bifocal, bicultural (v. multicultural), bicuspid (L cuspis, “point)), bifurcate (denominative, from L furca, “fork”), and bigamy (hybrid, from G γαμος, “marriage”). If the second element begins with a vowel, one may meet the related Latin combining form bin-^[5]: binocular, binaural. However, biovular —more easily read if spelled bi-ovular—is a term that describes the origin of fraternal twins.

Among the “other” Latin numeral words given in §124 (and note 1) we find the direct source of English primary, secondary, tertiary, quartile, decimal, singular, binary, ternary, centenary, and millenary. The commemorative terms centenary (100), sesquicentenary (150), and bicentenary (200) are used to mark significant dates in the history of cities and nations. Unlike those words, the adjectives centennial, sesquicentennial, and bicentennial are based on a modified form of the Latin noun annus, “year.” A millennium (adjective millennial) is a period of a thousand years. Even well-educated people often leave out an -n- in spelling the word millennium; don’t confuse it with millenary.

The root of Latin singuli (“one at a time,” E single) was combined with the root plic- (“fold”) to produce L simplex (< *sin-plic-s). So duplex, triplex, etc.^[6] The regular abstract nouns were simplic-itas and duplic-itas (E simplicity, duplicity, multiplicity). In medieval Latin, the 3rd declension adjective simplex developed a 2nd declension variant simplus, source of E simple. (So duplus, triplus > duple, triple.)