Why is the ninth month called September?
"small imaginary creature blamed for mechanical failures," oral use in R.A.F. aviators' slang from Malta, Middle East and India said to date to 1923. First printed use perhaps in poem in journal "Aeroplane" April 10, 1929; certainly in use by 1941, and popularized in World War II and picked up by Americans (e.g. "New York Times" Magazine April 11, 1943). Of unknown origin. Speculations in Barnhart are a possible dialectal survival of Old English gremman "to anger, vex" + the -lin of goblin; or Irish gruaimin "bad-tempered little fellow." Surfer slang for "young surfer, beach trouble-maker" is from 1961 (short form gremmie by 1962).
[origin unknown; probably modeled on goblin, with the first syllable perhaps fr Irish gruaimin, ''irascible little creature'']