Curious. In polish there are also two words. Moth is "ćma" and butterfly is "motyl". Funfact: There is also "ćmić" whichs kinda archaic,but can mean giving very small light (for example, embers), a very small but constant pain or shading/covering/dimming something.
And apparently the word comes from latin "tenebra". Quite dramatic, as it means the word has it roots in word for darkness itself. Quite a name for a small, mostly blind furry butterfly wannabe.