Speak one's thoughts audibly, as in We need flour, sugar, butter—I'm just thinking aloud. [Early 1700s]
Words That Are Older Than You ThinkThe first citation of "OMG" in the Oxford English Dictionary appears in a 1917 letter from the British admiral John Arbuthnot Fisher to Winston Churchill.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.