bumblebee (n.)youdaoicibaDictYouDict
also bumble-bee, 1520s, replacing Middle English humbul-be (altered by association with Middle English bombeln "to boom, buzz," late 14c.); echoic, from PIE echoic root *kem "to hum."
burden (n.2)youdaoicibaDictYouDict
"leading idea," 1640s, a figurative use from earlier sense "refrain or chorus of a song," 1590s, originally "bass accompaniment to music" (late 14c.), from Old French bordon "bumble-bee, drone," or directly from Medieval Latin burdonom "drone, drone bass" (source of French bourdon, Spanish bordon, Portuguese bordão, Italian bordone), of echoic origin.