Naš plan ovisi o vremenu.

Ovisi means “(it) depends”.

• The infinitive is ovisiti = to depend.
• In this sentence, ovisi is 3rd person singular, present tense:
  • ja ovisim
  • ti ovisiš
  • on/ona/ono ovisi
  • mi ovisimo
  • vi ovisite
  • oni/one/ona ovise

Here, the subject is naš plan (our plan), so we use ovisi = our plan depends.

With the verb ovisiti, Croatian normally uses the pattern:

• ovisiti o + locative = to depend on

So you say, for example:

• ovisi o vremenu – depends on the weather
• ovisi o tebi – depends on you
• ovisi o situaciji – depends on the situation

The preposition o in this meaning (“about / on” in the sense of dependency) always takes the locative case, so the noun after o must be in locative.

Vremenu is in the locative singular.

• The base (dictionary) form is vrijeme (neuter noun) = time / weather.
• Locative singular of vrijeme is vremenu (the j disappears):
  
  • Nominative: (to) vrijeme
  • Genitive: (bez) vremena
  • Dative/Locative: (o / prema) vremenu
  • Accusative: (za) vrijeme
  • Instrumental: (s) vremenom

So o vremenu = about/on the weather/time in locative.

This is a regular phonetic change for this type of noun.

For vrijeme:

• In oblique cases (like dative, locative, instrumental), the -je- often simplifies:
  • vrijeme → vremenu (dative/locative)
  • vrijeme → vremenom (instrumental)

You don’t say vrijemenu; standard Croatian drops the j here, giving vremenu.

It can mean both “time” and “weather” in Croatian; context decides.

In this sentence, Naš plan ovisi o vremenu, the natural interpretation is:

• “Our plan depends on the weather.”

Because plans typically depend on whether it will be sunny, rainy, etc., not on abstract time. If you wanted to stress time, you might clarify differently, e.g. Naš plan ovisi o tome koliko imamo vremena – “Our plan depends on how much time we have.”

In standard Croatian, the correct form is:

• ovisi o + locative → ovisi o vremenu

Many speakers do say ovisi od + genitive (e.g. ovisi od vremena) in everyday speech, but this is generally considered colloquial or non‑standard.

For proper Croatian, stick with:

• ovisi o vremenu (not od vremenu, not od vremena in formal usage).

Naš plan is the subject of the sentence.

• plan – a masculine singular noun in the nominative (subject form)
• naš – a possessive adjective meaning our, agreeing with plan in:
  • gender: masculine
  • number: singular
  • case: nominative

So literally: Our plan depends on the weather.

Naš is a possessive adjective derived from mi (we), and it must agree with the noun it modifies.

Here:

• naš plan – masculine singular nominative

Other examples:

• naša kuća (our house) – feminine singular
• naše dijete (our child) – neuter singular
• naši planovi (our plans) – masculine plural

So if you changed the subject:

• Naši planovi ovise o vremenu. – Our plans depend on the weather.

Yes, Croatian word order is relatively flexible, and O vremenu ovisi naš plan is grammatically correct.

• Naš plan ovisi o vremenu. – neutral, unmarked order.
• O vremenu ovisi naš plan. – puts more emphasis on “o vremenu” (on the weather). It feels like: It’s on the weather that our plan depends.

Both mean the same thing; the change mainly affects emphasis and style, not basic meaning.

No. Ovisiti is not used reflexively in this meaning.

• Correct: Naš plan ovisi o vremenu.
• Incorrect: Naš plan se ovisi o vremenu.

You simply use the verb ovisi with the subject and the prepositional phrase o + locative.