1 [mass noun] a substance used as a preparatory coat on wood, metal, or canvas, especially to prevent the absorption of subsequent layers of paint or the development of rust:apply three coats of primer [count noun]:new plaster should be treated with a primer
a cosmetic applied to the face before another product, intended to improve the coverage and lasting effect of the second product:it’s best to apply primer around the eye to help the make-up blend properly
2a cap or cylinder containing a compound which responds to friction or an electrical impulse and ignites the charge in a cartridge or explosive:the nitro-cellulose is ignited by the spark that comes from the primer
3a small pump for pumping fuel to prime an internal-combustion engine, especially in an aircraft:no more than four pumps of the primer usually suffice
4 Biochemistry a molecule that serves as a starting material for a polymerization process:the duplex RNA primer cannot initiate DNA replication
