noun

• The act of injecting, or something that is injected.
• A specimen prepared by injection.
• (category theory) A morphism from either one of the two components of a coproduct to that coproduct.
• (construction) The act of inserting materials like concrete grout or gravel by using high pressure pumps.
• (figuratively) The supply of additional funding to a person or a business.
• (mathematics) A relation on sets (X,Y) that associates each element of Y with at most one element of X.
• (computer security) The insertion of program code into an application, URL, hardware, etc.; especially when malicious or when the target is not designed for such insertion.
• (space science) The act of putting a spacecraft into a particular orbit, especially for changing a stable orbit into a transfer orbit, e.g. trans-lunar injection.
• (set theory) A function that maps distinct x in the domain to distinct y in the codomain; formally, a f: X → Y such that f(a) = f(b) implies a = b for any a, b in the domain.
• (medicine) Something injected subcutaneously, intravenously, or intramuscularly by use of a syringe and a needle.
• (medicine) Congestion (of a body part, with blood or other fluid), such as hyperemia.
• (internal combustion engines) Fuel injection: the pressurized introduction of fuel into a cylinder.
• (steam engines) The act of throwing cold water into a condenser to produce a vacuum.
• (steam engines) The cold water thrown into a condenser to produce a vacuum.