How Well Do You Know English Slang?
c.1300, "bed-clothing; white woolen stuff," from Old French blanchet "light wool or flannel cloth; an article made of this material," diminutive of blanc "white" (see blank (adj.), which had a secondary sense of "a white cloth." Wet blanket (1830) is from the notion of a person who throws a damper on social situations like a wet blanket smothers a fire. In U.S. history, a blanket Indian (1859) was one using the traditional garment instead of wearing Western dress.
Only 26,000 blanket Indians are left in the United States. ["Atlantic Monthly," March 1906]
c.1600, "to cover with or as with a blanket;" also "to toss in a blanket" (as punishment), from blanket (n.). Related: Blanketed; blanketing.