noun

• (uncountable, rare) Lemon juice.
  "[J]uſt at the laſt ſcald four or five ſpoonfuls of thick new cream, with a few drops of lemon or vinegar, muſhrooms pickled do well, […]"
• (slang) A defective or inadequate item or individual.
  "He didn’t realise until he’d paid for it that the car was a lemon."
• (Cockney rhyming slang, shortened from “lemon flavour”) Favor.
  "A thousand quid for that motor? Do me a lemon! I could get it for half that."
• (dated, fandom slang) A piece of fanfiction involving explicit sex.
  "I'd really like to know what people think of this and whether I should carry on writing lemons or go and hide under a rock somewhere."

adj

• (Cockney rhyming slang, from "lemon tart") Smart; cheeky, vocal.
  "Obviously Emin is not the first public figure to get lemon over tax increases."

verb

• (transitive) To flavour with lemon.
  "You can start the vegetables cooking while you are lemoning the fish."