burro (n.)

"donkey," 1800, from Spanish burrico "donkey," from Late Latin burricus "small, shaggy horse," probably from burrus "reddish-brown," from Greek pyrros "flame-colored, yellowish-red," from pyr (genitive pyros) "fire" (from PIE root *paewr- "fire"). Or, for its shaggy hair, from Late Latin burra "wool," a word of unknown origin.