seilleann-dé, noun = butterfly – (lit. “bee of God”)

Related words:
seilleann-mòr – bumble bee (lit. “big bee”)
seilleann-nimh – hornet (lit. “poison bee”)
seilleann-seimhid – snail
seilleannach – fulls of bees, teasing, capricious

There are also some interesting words for butterfly in Welsh:
iâr fach yr haf (lit. “summer chick”)
glöyn byw (lit. “living coal”)
pila-pala
bili-balo

In Irish, a butterfly is a féileacán – sounds like “failure can”, and in Manx it’s foillycan or follican – sounds like “foily can” as in a can covered in foil.