What is the X in X-mas?
Old English flea, from Proto-Germanic *flauhaz (cf. Old Norse flo, Middle Dutch vlo, German Floh), perhaps related to Old English fleon "to flee," with a notion of "the jumping parasite," or perhaps from PIE *plou- "flea" (cf. Latin pulex, Greek psylla; see puce).
Flea-bag "bed" is from 1839; flea circus is from 1886; flea collar is from 1953.
"A man named 'Mueller' put on the first trained-flea circus in America at the old Stone and Austin museum in Boston nearly forty years ago. Another German named 'Auvershleg' had the first traveling flea circus in this country thirty years ago. In addition to fairs and museums, I get as high as $25 for a private exhibition." ["Professor" William Heckler, quoted in "Popular Mechanics," February 1928. Printed at the top of his programs were "Every action is visible to the naked eye" and "No danger of desertion."]
Any of various small, wingless, bloodsucking insects of the order Siphonaptera that have legs adapted for jumping and are parasitic in the hair and feathers of warm-blooded animals.
David at the cave of Adullam thus addressed his persecutor Saul (1 Sam. 24:14): "After whom is the king of Israel come out? after whom dost thou pursue? after a dead dog, after a flea?" He thus speaks of himself as the poor, contemptible object of the monarch's pursuit, a "worthy object truly for an expedition of the king of Israel with his picked troops!" This insect is in Eastern language the popular emblem of insignificance. In 1 Sam. 26:20 the LXX. read "come out to seek my life" instead of "to seek a flea."