Spelling and Etymology
Why is the word hemorrhoid so difficult to spell? Most likely because doctors invent words that laypeople can't spell nor understand so that they can feel intellectually superior. Just kidding (sort of). Like a lot of medical terminology, the word hemorrhoid comes to us from the Greek with French and Latin modifications. And, like a lot of words that come to us from languages which have different letters and sounds than English, there are multiple possible ways to spell the word, each of which looks and sounds correct.
The word "hemorrhoid" originated in the late 14th century as the word emeroudis, which was from the 13th century Old French word emorroides, which in turn came from the Latin hæmorrhoidæ, a spelling which closely resembling the current British spelling of the word. This Latin word comes from the Greek "haimorrhoides," which is the plural of αἱμορροΐς (haimorrhois), which is a compound word formed from αἷμα (haima), meaning "blood," plus ῥόος (rhoos), meaning "a stream," or "a flowing".
The word haima, of course, is the root of words like hemaglobin, hematology, and hematocrit, all of which have to do with blood. The word rhoos comes from the Greek word rhein, meaning "to flow." This word sounds like it should have some connection to words such as rhinoplasty and rhinitis, which have something to do with the nose (Greek ῥίς=rhis). In fact, the word rhein is related to the English word rheum, from which we get words like rheumatoid and rheumatology, and it provides the ending for the word diarrhea. In fact, these two Greek roots (rhis=nose and rhoos=flow) are combined in the English word rhinorrhea, which means, naturally, "runny nose." In case you are wondering, the name of the Rhine River may also be vaguely related to this word.
How about the word "piles," which is a more colloquial term? It is thought that this word comes from the Latin word pila, meaning "balls" because of the round shape of the inflamed hemorrhoids.
Now, don't you feel smarter?!
In order to make sure that search engines direct traffic here, I am including a list of some incorrect spellings of the word hemorrhoid: hemeroid, hemoroid, hemerroid, hemorroid, hemerrhoid, rrhoids, roids. Feel free to send me your favorite misspelling to add to the list.
Sources:
The Online Etymology Dictionary