noun

• (usually countable, cooking, originally US) A small square piece of rich cake, usually made with chocolate.
  "Order for the brownie was placed but it took half an hour to prepare it."
• (uncountable, cooking, Australia and New Zealand) A sweet bread with brown sugar and currants.
  "It was an amusing sight to see the three of us, each with a huge hunch of “browny” (bread sweetened with brown sugar and currants) in one hand, and a lump of ice in the other, for there was no water within reach."
• (countable)
  "Thus, offer Brownie a piece of bread, a cup of drink, or a new coat and hood, and he flouted at it, and perhaps, in his huff, quitted the place for ever ; but leave a nice bowl of cream, and some fresh honeycomb, in a snug private corner, and they soon disappeared, though Brownie, it was to be supposed, never knew any thing of them."
• (countable)
  "He rose and jingled in his pockets for change and drew out two brownies. He went and set one on each of Monroe’s eyes[.]"

noun

• (British, Canada, Australia) A junior Girl Guide.
  "1958 July 14, Boot by a Brash Brownie, LIFE, page 124, In Toronto young Brownies of the Girl Guides, the Canadian girl scouts, stood in parade formation with full-fledged Guides."
• (US) A junior Girl Scout.
  "1952 March 24, Girl Scouts: They Are Observing Their 40th Birthday, LIFE, page 109, Any girl willing to follow the simple rules can join the Girl Scouts. As Brownies they will spend most of their time playing games and singing songs like the Brownie Smile Song: “I′ve something in my pocket; It belongs across my face, And I keep it very close at hand In a most convenient place.... I′m sure you couldn′t guess it If you guessed a long, long while, So I′ll take it out and put it on—It′s a great big Brownie smile!”"