Q: The word “indissoluble” popped out at me in one of David Denby’s New Yorker movie reviews. It’s not his fault, of course—it’s in the dictionary. But why does this word have a double negative prefix? Why not simply “insoluble”?
A: Don’t jump to conclusions. Each of these English words—“insoluble” and “indissoluble”—has only one negative prefix.
The story begins with two Latin words (solvere and dissolvere) that mean the same thing: to loosen or dissolve.
English got “soluble” from solvere (via the Late Latin solubilis) and “dissoluble” from dissolvere (via the Classical Latin dissolubilis).
When the adjective “soluble” entered English around 1400, it was a medical term that meant free from constipation (remember those Latin senses of solvere?).
In the 1500s, “soluble” took on the sense you’re asking about (capable of being dissolved), according to published references in the Oxford English Dictionary.
The OED’s earliest citation for this sense is from Polychronicon, a work by the Benedictine monk Ranulf Higdon that refers to a white salt “whiche, beenge soluble in the fyre, brestethe and brekethe in the water.”
As for “dissoluble,” the adjective entered English in the 16th century, meaning capable of being separated into elements or being destroyed.
The OED’s first citation is from Sir Thomas More’s Treatise on the Passion (1534): “The body being made of the earth, and mixte wyth other elementes, was of nature dyssoluble and mortall.”
It took about a century for the word to come to mean capable of being dissolved—that is, soluble.
The first OED citation, from The Art of Distillation (1651) by the English physician John French, says water passing through a mine “carryeth along with it some of the dissoluble parts of the mine.”
As for the negative versions, “insoluble” and “indissoluble,” the OED says, they’re simply the result of adding the negative prefix “in-” to “soluble” and “dissoluble.”
You’ll find entries for both negatives in The American Heritage Dictionary of the English Language (4th ed.) and Merriam-Webster’s Collegiate Dictionary (11th ed.), as well as the OED.
Although both are considered standard English, the one you prefer, “insoluble,” is by far the more popular, with 14.6 million hits on Google compared to not quite 1.6 million for “indissoluble.”
By the way, the Latin roots of these words have given us many other common words, including “absolve,” “dissolute,” “dissolve,” “resolve,” “solution,” “solve,” and “solvent.”
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