Questions & Answers about Flumen in mare fluit.
Flumen is nominative singular, which is the case normally used for the subject of a sentence.
We know it is the subject because:
- the nominative case commonly marks the doer or main thing being described
- the verb fluit is third person singular, so it matches a singular subject
- the meaning fits naturally: the river is what is flowing
So flumen = the river as the subject.
Flumen, fluminis is a third-declension neuter noun meaning river.
A learner may notice that it does not look like a first- or second-declension noun. That is because it belongs to the third declension, where noun forms are more varied. Its nominative singular is flumen, and its stem appears in forms like fluminis.