(n.) a dull or intermittent pain; (v.) to throb
When used as a noun, ache used to be pronounced as it’s written, with a “ch” sound, like “aitch”. Only the verb was pronounced with the harder “k” sound, “ake”, until the 1700s, when both the noun and the verb took the “k”.
So why? How? When? Where? Actually, scratch that last one, that’s not important.
Ache in all its forms derives from an Old English verb, acan. Very roughly speaking, it would have been pronounced as if rhyming with darken or harken—with an “ah” sound produced at the back of the mouth, and a hard “k” sound in the middle.
Ache was a strong (i.e. irregular) verb in Old English, meaning that it changed its vowel when conjugated (i.e. an ablaut formation). So the past tense of ache in Old English would once have been oc, and the past participle acen. Similar patterns survive in other strong Old English verb sets like take, took and taken, and shake, shook and shaken—but ache lost its ‘strength’ in the Middle English period, and steadily weakened (i.e. became more regular) to leave us with the ache and ached forms we use today.
At the same time all this was taking place, however, something else was happening too.
The verb form of ache in Old English may have been pronounced with a hard “k” sound, but the noun was different. It was spelled æce, or ece; although there was considerable variation in Old English vowel sounds, those initial Æ or E spellings show that the Old English noun ache was pronounced with a vowel closer to the front of the mouth than the harsher “ah” sound of the verb, acan.
Where did that distinction come from? It’s difficult to say, although we’re so far back in the mists of etymological time here that it’s possible this noun–verb/“e”–“a” distinction was already established in the Germanic languages even before English began to develop as a language in its own right in the fifth century. If that’s the case, then English would have simply inherited its two different forms of ache from its Germanic ancestors.
It’s a little beyond what concerns us here to sort that issue out, though—what really matters is the effect this vowel difference had on the “k” sound that followed it.
Brace yourselves, because here comes the science bit. Old English had a tendency to palatalize velar consonants when they happened to fall in the context of front vowels. (Linguists, feel free to skip ahead a few paragraphs. Everyone else, here’s what in the name of holy hell all of that means.)
Velar consonants are those produced using the soft palate, or velum, towards the back of the roof of the mouth. In English, the velar sounds are “k” and “g”; say them and you’ll feel your tongue rise up to meet the velum, blocking the flow of air through your mouth to produce the sound.
Palatalization is a process of phonological change in which more of the hard palate, closer to the front of the roof of the mouth, becomes involved in producing a sound. English has separate palatalized sounds too, in the form of “sh” and “tch”; say those and you should feel your tongue lift up a little further forward in your mouth, more distant from the velum.
Cut through all that linguistic jargon, then, and in essence Old English had a tendency to pronounce sounds like “k” and “g” as something more akin to “sh” and “tch” when they happened to appear alongside vowels produced towards the front of the mouth. The fact that the noun form of ache in Old English, æce or ece, was pronounced with a front vowel would ultimately have led to its central C being pronounced not like the hard “k” of the verb, but as a softer “tch” sound. So while the verb ache was pronounced like “arken” in darken in Old English, the noun ache came to be pronounced almost like the “etcha” in Etch-A-Sketch.
Nor was ache the only word in which noun–verb and “k”–“tch” distinctions like this were borne out. On Twitter, we mentioned the related pairs speak and speech, and bake and batch—but there’s also make and match, break and breach, wake and watch, and even stick and stitch. Delve into their histories and you’ll see Old English “k” sounds becoming palatalized, to produce a meaningful difference between the related verbs and nouns. But while all those pairs have retained this “k”–“tch” distinction to this day, ache has not. And for that, you can probably blame Samuel Johnson.
For many years, the verb ache retained its strong “k” sound, and was often spelled as such in written English; go back a few centuries, and you’ll find spellings like ‘ake’ and ‘acke’ were the usual form of the verb, reflecting retention of the Old English pronunciation. Likewise, the noun ache retained its “tch” sound—as in this brilliant play on words from Shakespeare’s Much Ado About Nothing, based around the similarity between the noun ache and the letter H:
BEATRICE: ’Tis almost five o’clock, cousin. ’Tis time you were ready. By my troth, I am exceeding ill. Heigh-ho!
MARGARET: For a hawk, a horse, or a husband?
BEATRICE For the letter that begins them all, H.
Towards the end of the 1600s, however, written records show both the noun and the verb ache were drifting towards one another and coalescing, both forms coming to be pronounced with the harder “k” sound. Ordinarily, this would have meant that ake would have become the standard spelling. But Samuel Johnson had other ideas.
In 1755, he published his monumental Dictionary of the English Language. Johnson’s Dictionary has two separate entries for ache: the noun ache and the verb ake. Under ake, however, Johnson wrongly explains that he believed the word to be of Ancient Greek origin, not Germanic origin, and points to its origin in a Greek word, akhos, meaning pain or distress. The verb ake, he ultimately decrees, should be “therefore more grammatically written ache.”
Johnson was wrong. But it’s hard to understate just how influential his dictionary ultimately became, and so his advocacy of the ‘ch’ spelling of both the noun and verb form of ache meant that ake—despite being the more rational and not at all etymologically inaccurate spelling—was doomed.
Long story short, then, the different noun and verb forms of ache came out of Old English’s treatment of “k” sounds in the context of different vowel sounds. Written and spoken English for a long time retained this distinction, to the extent that Shakespeare was able to make a pun about them in the early 1600s. By the end of the 1600s, however, the two forms were beginning to morph together, with the harder “k” sound appearing in both forms as it is today. Our spelling would have kept up with this change had Johnson and his peers not wrongly assumed the word to be Greek, and imposed a ‘ch’ spelling that really made no sense.
Frankly, it’s all a bit of a headache.