noun

• (uncountable) The act, process, or state of reinforcing or being reinforced.
  "If a journalist speaks for herself, let her say so. If something is true of "a few" or "some" or "many" or, even, "most" of us, then let her say that. It may cost a few extra modifiers, but it will prevent the unconscionable reinforcement of the myth that we are all alike."
• (countable) A thing that reinforces.
  "There's a website that can be a good learning reinforcement."
• (in the plural) Additional troops or materiel sent to support a military action.
  "Send in the reinforcements!"
• (uncountable, behavioral psychology) The process whereby a behavior with desirable consequences comes to be repeated.