-plus
Pronunciation
Forms
-plus (feminine -pla, neuter -plum); first/second-declension suffix[1]
Etymology
It is inherited from Proto-Italic *-plos, inherited from Proto-Indo-European *-pl(H)-o-.[1][2] De Vaan reconstructs Proto-Italic *dwiplo-, which became ⟨duplo-⟩, since Italic replaced ⟨dui-⟩ by ⟨du-⟩ in compounds with “two”, as in duplex.[2]
The root is uncertain.[2] Proto-Indo-European *pleh₁- (“to fill”) suits manipulus “a handful”, if it is from ⟨manu-plo-⟩, but fits the numerals less well;[2] Lindner proposes a root “to fold”, and de Vaan mentions a root “to approach” (“in two goes” > “double”), which he calls speculative.[2]
Cognate with Umbrian tupler (“two at a time”), Ancient Greek διπλόος (diplóos, “double”), ἁπλόος (haplóos, “single, simple”) and Old Irish díabul (“double”).[2]
Earliest recorded meaning
Plautus has simplus and duplus;[2] quadruplus and dupliō “twice the amount” appear in the Twelve Tables.[2]
Semantic evolution
The suffix makes multiplicative adjectives, “-fold”, from numerals: simplus “single”, duplus “double”, triplus “triple”, quadruplus “fourfold”.[2][1] From these come verbs and nouns such as quadruplāre “to quadruple” and quadruplātor, one who brings a criminal accusation, both in Plautus.[2]