Avoid the incorrect forms dilutent and dilutant. (1) Ingredient in a medicinal preparation that lacks pharmacologic activity but is pharmaceutically necessary or desirable. In tablet or capsule dosage forms, this may be lactose or starch; it is particularly useful in increasing the bulk of potent drug substances with a mass too small for dosage to allow manufacture or administration. May be a liquid for the dissolution of drug(s) to be injected, ingested, or inhaled. (2) Denoting that which dilutes; the diluting agent.