"something that causes terror," especially needless terror, 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.).
Germany was always a bugbear for France
buffoonery
Bufo
bug
bug off
bugaboo
bugbear
bug-bite
bugger
buggery
buggy
bughouse
