TWTS: "Primer" is pronounced "primer," unless you prefer "primer"
When we’re talking about a small book for teaching children to read, or really any short book that introduces a topic, there are two competing pronunciations of the word for that book.
One rhymes with "timer," while the other rhymes with “simmer.” For the sake of clarity, we’ll be using the spelling “primmer” to distinguish the second pronunciation from the first, however, they’re both actually spelled “primer.”
A listener from U of M Medical School named Kathy Spindler co-hosts a podcast about virology. Recently, another co-host said they didn’t know how to pronounce "primer." Kathy jumped in and explained that when you’re talking about a basic manual, like a Dick and Jane book, it’s pronounced “primmer.” If you’re talking about pre-treatment for painting or a key ingredient in DNA replication, it’s “primer.”
We realize that there are some people that wouldn’t use “primmer” at all and would simply use “primer” in all of the aforementioned contexts. However, “primmer” is out there, and Kathy wants to know how these two different pronunciations evolved.
What we're actually dealing with is two different words that come from two different sources.
The “primmer” pronunciation came into English from the Latin term "primarius" which meant "first.” This word can be traced back in written forms of English to the late 1300s. It originally referred to a Christian prayer book for laypeople (as opposed to clergy) that was often used to teach reading. By the 1500s, there are versions of these books that are only used to teach children to read.
Today you’ll see the “primmer” pronunciation used to refer to an introductory book on any subject, or even more generally, anything that serves as an introduction to a topic.
Later on in English, the word “primer” appears, formed from the verb “prime” and the suffix “er.” This verb meant to cover something, like wood or metal, with a preparatory coat of something, like paint. Thus, “primer” refers to the substance that primes. There are also some very specialized uses of “primer” related to engineering, firearms, physiology, biochemistry, etc.
In the U.S., these two words are often pronounced differently: “primmer” for the book, and “primer” for the paint pre-treatment and other things. In British English, both words are typically pronounced “primer.” The book meaning used to be pronounced “primmer,” but by the late 1800s, many people were using “primer” to refer to the book. By the early 20th century, usage manuals began noting that “primer” was becoming the more standard pronunciation.