primer

Primer is special paint that prepares and evens out a surface. If don't use primer, it will take three or four coats of paint to cover up the ugly bright orange color that's underneath.

Any way you use the word primer, it's a first step or preparation for something else. There's primer you use before painting, and an engine primer that prepares a machine to be started. In these examples, primer rhymes with timer. When primer describes an introductory textbook, it rhymes with dimmer. In the 14th century, a primer was a prayer book. This word comes from primus, the Latin word for first.