"forcing a fluid into a body" (with a syringe, etc.), early 15c., from Middle French iniection (14c.) or directly from Latin iniectionem (nominative iniectio), noun of action from past participle stem of inicere (see inject).
injection in·jec·tion (ĭn-jěk'shən)
The act of injecting a substance into a tissue, vessel, canal, or organ.
Something that is injected, especially a dose of liquid medicine injected into the body.
Congestion or hyperemia.