Unknown. First attested as a synonym of kaisla; the modern sense is probably from Elias Lönnrot's Flora Fennica (1860). Could be related to dialectal piuru (“beaver”) (< Old Swedish biur), but the semantic development would not be certain.
piuru
| Inflection of piuru (Kotus type 1/valo, no gradation) | |||
|---|---|---|---|
| nominative | piuru | piurut | |
| genitive | piurun | piurujen | |
| partitive | piurua | piuruja | |
| illative | piuruun | piuruihin | |
| singular | plural | ||
| nominative | piuru | piurut | |
| accusative | nom. | piuru | piurut |
| gen. | piurun | ||
| genitive | piurun | piurujen | |
| partitive | piurua | piuruja | |
| inessive | piurussa | piuruissa | |
| elative | piurusta | piuruista | |
| illative | piuruun | piuruihin | |
| adessive | piurulla | piuruilla | |
| ablative | piurulta | piuruilta | |
| allative | piurulle | piuruille | |
| essive | piuruna | piuruina | |
| translative | piuruksi | piuruiksi | |
| abessive | piurutta | piuruitta | |
| instructive | — | piuruin | |
| comitative | See the possessive forms below. | ||