-nus

• -ānus, -ēnus, -ernus, -iānus, -īnus, -rnus, -ūnus, -urnus (enlargements)

• (Classical) IPA^(key): /nus/, [nʊs̠]
• (modern Italianate Ecclesiastical) IPA^(key): /nus/, [nus]

From Proto-Italic *-nos, from Proto-Indo-European *-nós.

-nus (feminine -na, neuter -num); first/second-declension suffix

1. derives adjective nouns from verbs.

The suffix -nus is appended to a verbal root to form an adjective and nouns.

Examples:

magnus

plēnus

tribūnus

lignum

tignum

This suffix survived in inherited forms and became productive through its derivations (cf. infra) by metanalysis (e.g. starting points may be the class of u stem tribus, from which tribū-nus, later interpreted as trib-ūnus).

First/second-declension adjective.

Ultimately the same as the above, but apparently rebracketed at some point as *-sno- (extracted from words like *tris-no-, the original form of ternus).

-nus (feminine -na, neuter -num); first/second-declension suffix

1. suffix used to form distributive numerals.

In pre-Latin, the suffix *-nos (Classical Latin -nus) was attached to numeral adverbs, cardinal numerals, or numeral stems to form distributive numerals, such as

‎*dwis (“twice”) + ‎*-no- → ‎*dwisno-[1] → bīnus (“two each”) (equivalent to bis +‎ -nus).

‎*tris (“thrice”) + ‎*-no- → ‎*trisno-[2] → tr̥sno- → tr̥no- → ternus (“three each”) (equivalent to ter +‎ -nus).

*quaturs (“four times”)[3] → ‎*quatrus + ‎*-no- → ‎*quatrusno- → quatr̥sno- → quatr̥no- → quaternus (“four each”) (equivalent to quater +‎ -nus).

‎*seks (“six”) + ‎*-no- → ‎*seksno- → sēnus (“six each”) (equivalent to sex +‎ -nus).

At some point in pre-Latin, the suffix seems to have become extended to *-sno-, presumably as the result of rebracketing of forms like *tris-no- as *tri-sno-,[2] *dwis-no- as *dwi-sno- or *seks-no- as *sek(s)-sno-.[4] By the time of Classical Latin, *-s- before *-n- had been lost by regular sound change, but it caused any preceding nasal or plosive consonants to be deleted and the preceding vowel to be lengthened. Thus, it can be inferred that the *-sno- variant of the suffix was used to form words like the following:

‎septem (“seven”) + ‎*-sno- → ‎*septem-sno- → septēnus (“seven each”).

‎novem (“nine”) + ‎*-sno- → ‎*novem-sno- → novēnus (“nine each”).

‎dec(em) (“ten”) + ‎*-sno- → ‎*deksno- → dēnus (“ten each”).

The -ēno- found in decades such as vīcēnus, trīcēnus probably developed from -ent-sno-.[5]

Then the ending -ēnus seems to have been extended from some of the above forms and used as a third allomorph of this suffix to form some of the other distributive numerals:

‎centum (“hundred”) + ‎-ēnus → ‎centēnus (“one hundred each”)

‎septingentī (“seven hundred”) + ‎-ēnus → ‎septingentēnus (“seven hundred each”) (alternative form of septingēnus)

‎mille (“thousand”) + ‎-ēnus → ‎millēnus (“one thousand each”)

‎quot (“how many”) + ‎-ēnus → ‎quotēnus (“how many each”)

First/second-declension adjective (distributive, normally plural-only; short genitive plurals in -num preferred).

Via -ēnus:

• Catalan: -è
• Old Spanish: -eno

• Sihler, Andrew L. (1995) New Comparative Grammar of Greek and Latin, Oxford, New York: Oxford University Press, →ISBN
• Palmer, L.R. (1906) The Latin Language, London, Faber and Faber