-issimus

Meaning

1. morphemesuffixAdded to an adjective noun to form its superlative grade
   altus (“high”) + -issimus → altissimus (“highest”)
   fortis (“strong”) + -issimus → fortissimus (“strongest”)

Origins

Inherited from Proto-Italic *-isəmos, from Proto-Indo-European *-is-(t)m̥mós, from *-yōs (comparative suffix, zero-grade *-is) + *-(t)m̥mos (absolute superlative suffix). The latter is seen whole in -timus (e.g. intimus, extimus, citimus, ultimus, assimilated pessimus, optimus). The original form seems, however, to be *-m̥mós (see super, summus), which acquired an initial /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. *-isəmos > *-ismos > *-īmus) superlative grades in -īmus, -ēmus etc. (e.g. extrēmus, suprēmus) are also found. The expected development of *-(o)ism̥mos > *-erimus is nowhere to be found. The geminate /s/ may be the result of expressive lengthening or influence from specific forms similar to pessimus and endings in -errimus and -illimus.