bugbear: [16] Early references to bugbear suggest that it was a sort of bug – ‘frightening creature’ – conjured up to frighten naughty children. It is usually assumed that the second element of the word simply represents the animal ‘bear’, and that the frightening creature was represented as being in the shape of a bear. The modern sense ‘source of annoyance’ developed in the late 19th century.
1580s, a sort of demon in the form of a bear that eats small children, also "object of dread" (whether real or not), from obsolete bug "goblin, scarecrow" (see bug (n.)) + bear (n.).
