You can be overwhelmed, and since the 1950s you can also be underwhelmed. But it’s been quite a long time since you — or anything else — has been simply whelmed. Although in fact, people haven’t been whelmed all that often.
“Whelm” used to be a common word; it was used in medieval England to mean a capsized boat or ship. “Cursor Mundi” is an anonymous poem from the 1300s that includes the line “Þaa sori loked ai sua for-suonken, Quen þe scip suld quelm and drunken.” OK, you’re right, it’s Middle English and pretty obscure, but “quelm” is “whelm.” This more accessible example comes from Robert Fabyan’s 1516 New Cronycles of Englande and of Fraunce: “By the Mysgydynge of the Sterysman he was set vpon the Pylys of the Brydge, and the Barge whelmyd.”
The word “whelm” was also used to mean turning a boat upside-down on land in order to use it as a cover for something. It didn’t take long for “whelm” to mean using anything as a cover. Here’s John Palsgrave, in 1530, using “whelm” that way: “Whelme a platter upon it, to save it from flyes.” Three centuries later, in 1854, Anne Elizabeth Baker used “whelm” the same way: “Whelm that dish over them currants.”
“Whelm” comes from an even older word: “whelve.” “Whelve” meant pretty much the same thing as “whelm,” and comes from Old English, where it was “hwylfan.” The two words were evidently used interchangeably, as the 1706 New World of Words dictionary pointed out in the definition: “To Whelm or Whelve, to cover.”
There was also a noun form of “whelm,” and it had two meanings. The first was an unusual sort of thing, or at least it seems unusual today. If you had a little watercourse or trough, for example, to direct water to your garden, or away from your house, you could cover it with, say, half of a hollowed-out tree trunk. Whatever you used to make that cover, it was called a “whelm.” You might also use a whelm as a sort of bridge to be able to cross your irrigation ditch, as Arthur Young suggested in his 1797 advice to farmers: “I strongly recommend these carrier ditches to be open, though at the expence of a whelm at the bottom of a field where a cart-way is necessary.” Because a whelm covered water, that led to the first usage of “overwhelm” — a flooded watercourse was “overwhelmed.”
The second meaning of the noun “whelm” also had to do with water, but in almost an opposite sense. If there was a flood or even a big wave, that surge of water was called a “whelm.” This sense of “whelm” didn’t come into use until the 1800s. Algernon Charles Swinburne used it in 1888: “They sink in the whelm of the waters.”
As for “underwhelm,” it first appeared in the 1956 book Giant Corporations: Challenge to Freedom: “He wrote..commending the action of one of the giant corporations for a…price reduction at a time when prices were rising. I was underwhelmed, and investigated.”
The word caught on, and is still in use today. But its use, compared to “overwhelm,” is underwhelming. According to Google’s Ngram Viewer, usage of “overwhelm” (which is slowly increasing) is orders of magnitude greater than that of “underwhelm”, which constituted only 0.0000001% of all the words printed in books from 1999 to 2000. “Overwhelm” accounted for a whopping 0.001%! But “cover”, which used to be a synonym for both “whelm” and “overwhelm”, accounted for almost 0.007%. None of these can compete with a fan favorite like “the” — 5% of all the words in books in those years were “the.”