-uus

From Proto-Finnic *-uc. The declension has been massively reworked by analogy.[1]

• IPA^(key): /-uːs/, [-uːs̠]

-uus (front vowel harmony variant -yys)

1. Forms nouns from adjectives, expressing a quality.

   -uus

   punainen (“red”) → punaisuus (“redness”)

   nerokas (“ingenious”) → nerokkuus (“ingenuity”)

   -yys

   pyhä (“holy”) → pyhyys (“holiness”)

   pitkä (“long”) → pituus (“length”) *not pitkyys

   -us

   hauras (“brittle”) → hauraus (“brittleness”)

   kaunis (“beautiful”) → kauneus (“beauty”)

   komea (“handsome”) → komeus (“handsomeness”)

   -ys

   leveä (“wide”) → leveys (“width”)

As a main rule, the suffix is added to the stem of the adjective, replacing any final vowel:

• kova (“hard”) → kovuus (“hardness”)
• kylmä (“cold”) → kylmyys (“coldness”)
• paksu (“thick”) → paksuus (“thickness”)
• suuri (“big”) → suuruus (“size”)
• sinise- (“blue”) → sinisyys (“blueness”)

The stem usually remains in the strong grade, but some exceptions remain as evidence of the original short vowel. In particular, all derivatives based on comparatives show the weak grade, e.g. alempi (“lower”) → *alemmus > alemmuus (“lowerness”), rather than ˣalempuus.

As noted above, the suffix additionally appears shortened to -us whenever it is preceded by a second vowel. Note that this includes contracted long vowels, as in *harmaɣa > harmaa (“gray”) → harmaus (“grayness”). Derivatives from adjectives ending in -is may in some cases show an unexpected alternation to -e-, as in the above-seen kauneus in place of expected ˣkaunius.

Some exceptions to this overall scheme occur, e.g. äiti (“mother”) → äitiys (“motherhood”), in place of expected ˣäityys. Very rarely, both allomorphs may even occur in parallel, e.g. lapsi (“child”) → lapsuus (“childhood; period of life”), yet lapseus (“childhood; state of being a child”).

• suu

From Proto-Finnic *-uc. Cognates include Finnish -uus and Estonian -us.

• (Ala-Laukaa) IPA^(key): /-uːs/, [-uːz̠]
• (Soikkola) IPA^(key): /-uːs/, [-uːʒ̥]

-uus (front vowel variant -yys)

1. Forms nouns from adjectives, expressing a quality; -ness

   ‎syvä (“deep”) + ‎-uus → ‎syvvyys (“depth”)

• The suffix is always appended to the oblique stem.
• When following a short stressed syllable, the long form -uus is used. In all other cases, the alternative form -us is used instead:

  ‎pitä- + ‎-uus → ‎pittuus

  ‎vanh- + ‎-uus → ‎vanhus

• Note that since the suffix -kas always carries secondary stress, the derivatives in -uus also always contain a long vowel:

  ‎voimakka- + ‎-uus → ‎voimakkuus

• V. I. Junus (1936) Iƶoran Keelen Grammatikka‎, Leningrad: Riikin Ucebno-pedagogiceskoi Izdateljstva, page 58

• -vus

From the Proto-Indo-European suffix *-wós‚ from the perfect active participle suffix *-wōs.

• (Classical) IPA^(key): /u.us/, [uʊs̠]
• (Ecclesiastical) IPA^(key): /u.us/, [uːs] (stressed on the antepenult)

-uus

1. forms adjectives on verbal stems

   contiguus, succiduus, vacuus

• Originally forming the perfect active participle, as in ambiguus (“having wandered”), mortuus (“having died”), vacuus (“having been empty”).
• The form -vus is used after vowels, l, and r, and -uus after all other other consonants, with the exception of qu. In this last case, the form -us is used.

First/second-declension adjective.