Q I hear people use “grotesque” when they really, to my mind, mean “gruesome.” Are these words really interchangeable? For example, should one call a devastating outbreak of some killer disease “a grotesque nightmare” or “a gruesome nightmare”? – P.D., Caldwell, Idaho

A: In one of Arthur Conan Doyle’s Sherlock Holmes stories, Holmes asks Dr. Watson, “How do you define the word ‘grotesque’?” Watson suggests, “Strange – remarkable,” but Holmes doesn’t entirely agree. “There is surely something more than that; some underlying suggestion of the tragic and terrible,” he says.

Watson is defining “grotesque” in its purest historical form. “Grotesque” comes from “grotta,” the Italian word for “cave.” During the Italian Renaissance, “pitture grottesche” were what the Italians called the exotic paintings found in caverns unearthed in the excavation of Rome. Later on, a style of decorative art that incorporated fantastic combinations of human and animal forms interwoven with strange fruits and flowers, reminiscent of the Roman “cavern pictures,” was called simply “grottesca” in Italian. The Italian word soon worked its way into English. Our noun “grotesque” still refers to a style of decorative art that distorts the natural – or, in a broader sense, to anything that we might describe by the adjective “grotesque.” The adjective first appeared in English at the beginning of the 17th century.

So the question then becomes, what are the limits of the grotesque? Synonyms for the adjective are “bizarre,” “fantastic,” “weird,” “outlandish” and “fanciful.” “Grotesque” emphasizes distortion of the natural usually to the point either of ridiculous ugliness or ludicrous caricature. Sometimes the word suggests an absurdly irrational combination of things that are incompatible, as in “in this war-torn state it is grotesque to use peacetime standards for measuring freedom of speech.”

The other “g” words – “gruesome,” “grisly,” “gross” and “ghastly” – really aren’t close synonyms of “grotesque,” but it’s apparent that the boundaries blur at times. Thus, you might read of “the grotesque inhumanity of his attacker.” How acceptable you find such usage may depend on whether you consider things that are horrific and revolting – or, in Sherlock Holmes’s phrase, “tragic and terrible” – to be strange or unnatural.

This column was prepared by the editors of Merriam-Webster’s Collegiate Dictionary, Tenth Edition. Readers may send questions to Merriam-Webster’s Wordwatch, P.O. Box 281, 47 Federal St., Springfield, MA 01102.