The Negative Numeral Nijedan
When you want to express the absolute absence of something—"not a single one" or "none"—you use the negative numeral nijedan. It is formed by attaching the prefix ni- to the number jedan (one).
Because it is based on jedan, nijedan acts like an adjective. It must agree with the noun it modifies in gender and case. Furthermore, Croatian enforces double negation: when you use nijedan, the main verb of the sentence must also be negative.
The Indefinite Numeral Ijedan
Similarly, adding the prefix i- creates ijedan, which translates to "a single one" or "any".
While nijedan is used for negative statements, ijedan is primarily used in questions or conditional clauses (if-statements) to emphasize "even one" or "any at all."
Declension Like Jedan
Because both nijedan and ijedan are built from jedan, their endings change to match the noun exactly as jedan does.
For masculine inanimate nouns like bunar (well), the accusative form is the same as the nominative.
For feminine nouns like oaza (oasis), the accusative ending becomes -u (nijednu, ijednu).
For neuter nouns like priviđenje (mirage), the nominative and accusative ending is -o (nijedno, ijedno).
Finally, if you use the verb form nema to say "there isn't" or "there is no," the noun that follows must take the genitive case. The numeral will take the masculine/neuter genitive ending -og(a).
