From Old Norse fiðrildi from the older term fífrildi, from Proto-Germanic *fifaldǭ *fīfildǭ (“butterfly”), from Proto-Indo-European *pāpel-, *pe(i)pel- (“butterfly”). The term fiðrildi came through the folk etymology that it was related to the Old Norse word fiðri (“feathers”) (compare the more modern Old Norse fiðr), from which the Icelandic fiður (“feathers, down”) came.
Cognate with Old High German fīvaltra (> Middle High German viveltre > German Falter); Old English fīfalde or fifalde; Swedish fjäril; Norwegian fivrelde or fibrelde and Latin pāpiliō.
fiðrildi n (genitive singular fiðrildis, nominative plural fiðrildi)
| singular | plural | |||
|---|---|---|---|---|
| indefinite | definite | indefinite | definite | |
| nominative | fiðrildi | fiðrildið | fiðrildi | fiðrildin |
| accusative | fiðrildi | fiðrildið | fiðrildi | fiðrildin |
| dative | fiðrildi | fiðrildinu | fiðrildum | fiðrildunum |
| genitive | fiðrildis | fiðrildisins | fiðrilda | fiðrildanna |