verb

• (intransitive) To shout extended boos derisively.
  "When he took the podium, the crowd booed."
• (transitive) To shout extended boos at, as a form of disapproval or derision.
  "The protesters loudly booed the visiting senator."

noun

• (US, Canada, African-American Vernacular, slang) A close acquaintance or significant other.
  "A tall, hooded young woman, clutching a newspaper article, delivered a note to the judge. “My name is Sunkist,” she wrote, “Lionel R. Harris is my boyfriend. Lewis shot my Boo and it was not self-defense . . . . Judge and jurors please listen to me I am 17 years of {age} and a good young lady and my Boo got killed for nothing.”"

noun

• (slang) Cannabis.
  "[…] sexually promiscuous girl who smoked boo all day and socialized with junkies when she wasn't busy banging away in bed […]"

verb

• (now rare, Northern England, intransitive) To make a sound characteristic of cattle; to moo.
  "The cow's tether is put about the neck of the individual who has lost the cow, and he must go about booing like a cow till atonement is made."