A vial is a very small bottle, usually glass, made to hold a small amount of liquid — medicine, a vaccine, blood taken for a test, perfume, or a chemical in a laboratory. The size is the point: a vial holds a dose or a sample, not a drink. Many have a rubber top that a needle goes through, so a nurse can draw the liquid out without opening the bottle. In stories, especially fantasy stories and older writing, a vial is what a potion or a poison comes in, so the word carries a slight feeling of something precious, dangerous or carefully measured. You will meet it in the news whenever vaccines are discussed: "each vial contains six doses". It is a countable noun: one vial, three vials, a vial of blood. There is another spelling, phial, which is the same word and means the same thing; phial looks older and more literary, and vial is the normal spelling today, especially in American English. It can also be used as a verb, to vial something, meaning to put it into vials, but that is rare and only in factory or laboratory writing.