Vaccine   
A substance used for injection that contains part of the antigen from an infectious agent. It protects against infection from that organism in the future by stimulating the immune response to it.

Venipuncture   
Puncturing the vein in order to obtain blood samples, to start an intravenous drip, or to give a medication.

Vesicant   
An intravenous medication that, if leaked into tissues, could cause pain, selling, tissue damage, and destruction.

Virilism   
Masculinizing condition occurring in women, which may include infrequent menstrual periods, cessation of menstrual periods before menopause, hoarse voice, and appearance of facial hair.

Virus   
A tiny infectious agent that is smaller than bacteria. The common cold is caused by a virus. For example, herpes simplex (cold sore).