The definition of intravenous is into a vein.
When you use a needle to inject heroin directly into your vein, this is an example of intravenous drug use.
in, or directly into, a vein or veins: an intravenous injection
Origin of intravenousintra- + venous
Within or administered into a vein.
A drug, nutrient solution, or other substance administered into a vein.
- Inside the veins.
(uncountable) (abreviated as IV)
From intra- + venous.