-plus

From Proto-Italic *-plos, cognate with Ancient Greek -πλόος (-plóos) or -πλός (-plós) (as in διπλός (diplós)), the second element of Old Irish díabul (“double”)^[1] and possibly Proto-Germanic *twīflaz (“doubt”). From an unclear root of the form *pl(H), possibly from Proto-Indo-European *pleh₁- (“to fill”) or Proto-Indo-European *pelh₂- (“to approach”)^[1] or Proto-Indo-European *pel- (“to fold”), source of Proto-Germanic *-falþaz (“-fold”).^[2] Compare also -plex.

• (Classical Latin) IPA^(key): /plus/, [pɫ̪ʊs̠]
• (modern Italianate Ecclesiastical) IPA^(key): /plus/, [plus]

-plus (feminine -pla, neuter -plum); first/second-declension suffix

1. -times, -fold, suffix used to form proportional numerals

The similar multiplicative suffix -plex tends to be used adjectivally to describe something composed of or possessing multiple parts, whereas the proportional suffix -plus tends to describe a ratio of size or quantity relative to something else ("so many times as much, so many times as large") and is often used in the neuter singular form as a noun or an adverbial accusative. The ending -plus is only attested in Classical Latin for a small set of numbers, perhaps only simplus (“simple”), duplus (“twice as much”), triplus (“three times as much”), quadruplus (“four times as much”), octuplus (“eightfold, eight times as much”), and sēscuplus (“one-and-a-half times as much”).

It can be found attached to other numbers in postclassical texts, with various analogical alterations in form. For example, aside from -uplus as in octuplus, the suffix can be found in the forms:

• -cuplus (from rebracketing of decuplus, possibly also of quīncuplus), as in nōncuplus (“ninefold”), sexcuplus (“sixfold”)
• -ecuplus, probably by rebracketing of decuplus, seen in tens (such as vīgecuplus or vīcecuplus (“twentyfold”), quadrāgecuplus (“fortyfold”), octōgecuplus (“eightyfold”), from vīgintī, quadrāgintā, octōgintā) and in millecuplus (“thousandfold”)

Several numbers show multiple alternative formations. The ordinal numerals seem to have influenced some forms, such as quīntuplus (“fivefold”), sextuplus (“sixfold”), nōnuplus (“ninefold”) from quīntus (“fifth”), sextus (“sixth”), nōnus (“ninth”).

First/second-declension adjective.