(noun)
a cosmetic make-up product that is put on the skin of the face before any other products, in order to make subsequent products longer-lasting or more effective;
e.g. She applied a layer of primer to her cheeks.
(noun)
a device that contains a substance that can ignite the charge of an explosive;
e.g. In this machine, the primer generates a spark to start up the engine.
(noun)
in biochemistry, a small molecule, especially a small section of RNA or DNA, that serves as the starting point for the formation of more of the molecule by a polymerization process;
e.g. They selected a primer that would help them isolate the gene of interest.
(noun)
a small section of text, for example a short book used to teach children how to read, or a brief introduction to a field of study;
e.g. The students were given a primer of the period of history they would be studying.