Etymology
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pecker (n.)

1690s, "one who or that which pecks," agent noun from peck (v.); slang sense of "penis" is from 1902, according to OED "chiefly U.S." OED adds that the British colloquial sense of "courage, resolution" (in keep your pecker up, 1853) is "commonly avoided by British travellers in the U.S."

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