“Ensure” and “insure” have different spellings and meanings, but that wasn’t always the case. For years, the terms were no more than spelling variations with the same meaning, and they only developed distinct definitions in the mid-19th century. However, it’s still easy to mix up the words, given their similar spellings and pronunciations, so here’s what you should know about how they differ.
“Ensure” came about in the late 14th century, derived from the Anglo-French enseurer, meaning “make sure.” By the middle of the 15th century, “insure” developed as an alternate spelling. It wasn’t until the mid-1800s that some writers suggested giving the terms distinguishable meanings. An entry in an 1871 writing guide suggested “that each of these words … shall become a distinct word, instead of being as now a various spelling.” Thus, unique definitions for each word developed.
“Ensure” is now defined by Merriam-Webster as “to make sure, certain, or safe,” while “insure” relates primarily to insurance and is defined as “to provide or obtain insurance on or for.” Because of this, many usage guides suggest using “ensure” in reference to guarantees of a more general nature, and using “insure” when talking about financial matters.
As the difference between the two is so nuanced, you may be wondering if it’s ever OK to use them interchangeably, and technically, the answer is “not really.” While the terms imply similar things, they’re clearly distinguishable from one another and should be used in separate contexts. Of course, it’s almost impossible to tell the difference in a spoken conversation, but when it comes to written text, it’s good to ensure that you use the correct word each time.
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