-issimus

• -issumus, -simus, -īmus

Via Proto-Italic *-isemos, from Proto-Indo-European *-is- (zero-grade of *-yōs (“intensive/comparative suffix”)) + *-(t)m̥mo- (“absolutive suffix”). The latter is seen whole in -timus (e.g. intimus – extimus, citimus – ultimus, dissimilated pessimus – optimus). The original form seems, however, to be *-m̥mo- (cf. super – summus, Gothic 𐌹𐌽𐌽𐌿𐌼𐌰 (innuma, “innermost”)), with acquired t from the paradigm -ter- – -timus- (e.g. exter – extimus), and is cognate with Proto-Germanic *-umô (source, via metanalysis, of English -most). By various sound changes (e.g. *-isemos > *-ismos > -īmus) superlative grades in -īmus, -ēmus etc. (e.g. extrēmus, suprēmus) are also found.

The expected alteration of *-(o)ism̥mos to *-erimus is nowhere to be found. The -ss- may be an example of expressive lengthening of the *-s- or influence from specific forms as pessimus and endings in -errimus and -illimus.

• (Classical) IPA^(key): /ˈis.si.mus/, [ˈɪs.sɪ.mʊs]
• (Ecclesiastical) IPA^(key): /ˈis.si.mus/

-issimus m (feminine -issima, neuter -issimum); first/second declension

1. added to an adjective noun to form its superlative grade

   ‎altus (“high”) + ‎-issimus → ‎altissimus (“highest”)

   ‎fortis (“strong”) + ‎-issimus → ‎fortissimus (“most strong”)

• Stems in -ro- and -lo- instead take the suffix -errimus and -illimus respectively (e.g. *polkros (pulcher) > *polkrisemos > *polkr̥semos > *polkersimos > pulcherrimus).
• Some adjective nouns have irregular superlative grades form other roots or compositions (e.g. bonus – optimus, malus – pessimus, magnus – maximus).

First/second declension.

• -ior

• Catalan: -íssim
• Francoprovençal: -issimo
• French: -issime, -îme
• Galician: -ísimo
• Italian: -issimo
• Portuguese: -íssimo
• Spanish: -ísimo

• Sihler, Andrew L. (1995) New Comparative Grammar of Greek and Latin, Oxford, New York: Oxford University Press, →ISBN
• 1865, Schultz, Ferdinand, Lateiniſche Sprachlehre zunächſt für Gymnasien bearbeitet [Latin grammar adapted primarily for grammar schools], 6th edition, Paderborn, §67, pages 76-77:

  Die Superlativendung issimus ſchrieb man in der Vorauguſteiſchen Zeit auch vielfach issumus (ebenſo errumus, illumus; vrgl. §. 4. Anm. 2.), und ſo ſchreiben auch heut zu Tage viele Kritiker in den Ausgaben namentlich der Komiker, des Salluſt, und auch wohl des Cicero.

  The superlative ending issimus is also written frequently in the pre-Augustan era as issumus (likewise errumus, illumus; cf. §4 annotation 2.), and so too do many critics write today particularly in the editions of the comics, of Sallust, and indeed of Cicero.