noun

• Any small fish.
• Any small fish.
  "In quiet, sheltered places, where the water is clear but does not run too swiftly, the ‘minnie,’ as the stickleback is locally called, makes its nest by the bank. […] On these fibres the ova are deposited, and they are then either purposely partly covered with sand by the minnie, or else the particles that are brought down by the current gather over the bundle of fibres and conceal it, excepting one small spot."
• (figuratively) A person or thing of relatively little consequence, importance, or value.
  "Let him denie that there was another shewe made of the little minnow his Brother, Dodrans Dicke, at Peter-houſe, called, Duns furens. Dick Harvey in a frenſie."
• (fishing) An artificial bait in the form of a small fish.
  "[…] I have (which I will show you) an artificial minnow, that will catch a trout as well as an artificial fly, and it was made by a handsome woman that had a fine hand, and a live minnow lying by her: […]"

adj

• (rare) Very small; tiny.