The Oxford English Dictionary word of the day is foo fighter:
Any of various unidentified lights encountered by airborne forces during the Second World War (1939–45), interpreted variously as enemy weapons, natural phenomena, or alien spacecraft.The term has its origin in the nonsense word foo, a staple of Bill Holman’s comic strip Smokey Stover (one of the great comic strips of my childhood). Alas, the OED misspells Stover’s first name.
Silence is FOO! (’t Is Goud)
Smokey Stover Online (full of foo and notary sojac)
[Do fans of Foo Fighters generally know the origin of the band’s name?]