Abstract Nouns in -ost

The suffix -ost is one of the most productive word-building tools in Croatian: take an adjective, add -ost, and you get an abstract noun meaning roughly "the quality of being that adjective" — the exact job English does with -ness and -ity. The bonus for the learner is that -ost is a double shortcut: it tells you the meaning ("-ness") and it tells you the gender and declension — every -ost noun is feminine and follows the i-declension. Recognise the suffix and you know almost everything about the word at a glance.

How -ost builds a noun

The mechanism is mechanical. Start from an adjective (usually its base masculine form, sometimes with a small stem adjustment), attach -ost, and you have a feminine abstract noun:

Notice the small adjustments. Adjectives with a fleeting -a- lose it before -ost: vrijed-a-n → vrijednost, sposob-a-n → sposobnost, ljubaz-a-n → ljubaznost, sigur-a-n → sigurnost. And moguć keeps its palatal ć: mogućnost. The pattern is regular enough that, once you know the adjective, you can usually predict the noun.

All -ost nouns are feminine i-declension

This is the half of the shortcut that saves you from the gender trap. Because -ost nouns end in a consonant (-t), a beginner's first instinct is to call them masculine. They are feminine, and they decline in the i-declension — the same pattern as noć and stvar. The genitive singular is -osti, and that -i runs through most of the paradigm.

Two things to note. First, the instrumental singular offers the i-declension choice between plain -osti and the contracted -ošću (mladošću, radošću, mogućnošću) — the -ošću form is the more elegant, written-register variant and is very common. Second, many -ost nouns are pure abstractions (mladost, starost) that rarely appear in the plural; but countable ones like mogućnost ("possibility, option") and vrijednost ("value") pluralise normally (mogućnosti, vrijednosti).

Related abstract suffixes

-ost is the biggest abstract-noun factory, but not the only one. Three relatives are worth knowing because they cover meanings -ost does not, and they each carry their own gender and declension.

-ina (feminine, -a declension)

The suffix -ina also turns adjectives into abstract nouns, often ones denoting a measurable degree or dimension — and unlike -ost, these are -a declension feminines (genitive -ine), so they take the clean accusative -u.

-oća (feminine, -a declension)

-oća is a smaller suffix forming abstracts mostly about physical qualities, again -a declension feminine:

-stvo (neuter)

For a contrast, the suffix -stvo builds neuter abstracts, typically from nouns rather than adjectives, naming a state, group, or domain. It declines as a plain neuter (-o type, genitive -stva):

How this differs from English

English does almost exactly the same thing — kind → kindness, able → ability, young → youth — so the concept of an abstract-noun suffix is completely familiar. The difference is that English abstract suffixes carry no gender or declension information, whereas Croatian's do: -ost simultaneously hands you "-ness," "feminine," and "i-declension." That is more information per suffix, and it works in your favour once learned. The one place English intuition misleads you is the consonant ending: an English speaker reads the final -t of mladost as neutral, but in Croatian a consonant ending normally signals masculine — so you must consciously override that instinct and remember that -ost is always feminine.

Common Mistakes

Key Takeaways

• -ost turns an adjective into a feminine abstract noun meaning "-ness/-ity": mlad → mladost, moguć → mogućnost, vrijedan → vrijednost. It is highly productive.
• Every -ost noun is feminine i-declension (genitive -osti), with the instrumental singular as -osti or the contracted -ošću (mladošću, radošću).
• Adjectives with a fleeting -a- drop it before -ost: vrijedan → vrijednost, sposoban → sposobnost, siguran → sigurnost.
• Related abstracts differ in gender/declension: -ina and -oća are -a declension feminines (brzina, čistoća), while -stvo is neuter (prijateljstvo).
• The suffix is a double shortcut: it gives you the meaning and the gender/declension at once. Watch only the consonant-ending instinct, which falsely suggests masculine.