The word comes straight from the Old English butorfloge, which means butterfly, according to the Oxford English Dictionary. While modern Dutch and German use different words (vlinder and Schmetterling), the common name frequently varies significantly between otherwise closely related languages. However, similar names in Old Dutch and Old High German demonstrate that the name is ancient. The bright yellow male of the brimstone (Gonepteryx rhamni) could be the source of the name. Another possibility is that during the grass-growing spring and summer butter season, butterflies were flying in meadows.

Around 200 million years ago, the Triassic-Jurassic boundary is where the earliest Lepidoptera fossils were found.Unlike moths, which are not monophyletic (forming a single clade), butterflies evolved from moths. Protocoeliades kristenseni, a member of the family Hesperiidae (skippers), is the oldest known butterfly. It is approximately 55 million years old and comes from the Danish Fur Formation, which is from the Palaeocene.

The macrolepidopteran suborder clade Rhopalocera of the order Lepidoptera, which also includes moths, is where their scientific classification falls.