Genuine, not a sham. The expression comes from the yard-goods industry, where a seller would claim that a piece of cloth was 100 percent wool and measured fully a yard, in contrast to inferior material and short measures.

Thoroughgoing, complete. The term, which dates from at least the sixteenth century, alludes to cloth made from wool that was dyed while raw (before it was spun) instead of being dyed piece by piece. The color therefore was “true” throughout, and this concept was transferred to other kinds of genuineness. “In half an hour he can come out an original democrat, dyed in the wool,” said Daniel Webster in a speech (Feb. 10, 1830). It has been a cliché since the early 1900s.

To hoodwink or deceive someone. This term comes from—and long survives—the custom of wearing a wig (except in the British legal system, where judges and barristers still do so). One writer suggests that it alludes to the slippage of the wig of a judge, who is temporarily blinded by a clever lawyer. In any event, it was used figuratively in a quite general way from the early nineteenth century on, on both sides of the Atlantic. “He ain’t so big a fool as to have the wool drawn over his eyes in that way,” wrote Frances M. Whitcher (The Widow Bedott Papers, 1856).