“Originating from Irish, it was meant to represent a slightly different pronunciation of the “th” sound, more like that in ‘thought’ or ‘thing’ as opposed to the one found in ‘this’ or ‘them.’ (The first is the voiceless dental fricative, the second is the voiced dental fricative).
“Note that, depending on your regional accent, there may not be much of a difference (or any at all) in the two pronunciations anyway, but that’s Modern English. Back in the old days, the difference was much more distinct. As such, you’d often see texts with both eth and thorn depending on the required pronunciation. Before too long, however, people just began using thorn for both (and later ‘th’) and so eth slowly became unnecessary.”
The sad story is that this most useful letter didn’t make it into the final cut for our 26-letter alphabet. The other far-flung rejects come from Iceland, Rome, and elsewhere. A must-read over at mental floss features a few more.
Here are a couple favorites:
Have you ever seen a place that calls itself “ye olde whatever”? As it happens, that’s not a “y”, or, at least, it wasn’t supposed to be. Originally, it was an entirely different letter called thorn, which derived from the Old English runic alphabet, Futhark.
Thorn, which was pronounced exactly like the “th” in its name, is actually still around today in Icelandic. We replaced it with “th” over time—thorn fell out of use because Gothic-style scripting made the letters y and thorn look practically identical. And, since French printing presses didn’t have thorn anyway, it just became common to replace it with a y. Hence naming things like, “Ye Olde Magazine of Interesting Facts” (just as an example, of course).
And here’s the old familiar “ash,” as in Cæsar.
What you may not know, however, is that at one time the ae grapheme (as it’s now known) was an honorary English letter back in the days of Old English. It still had the same pronunciation and everything, it was just considered to be part of the alphabet and called “æsc” or “ash”after the ash Futhark rune, for which it was used as a substitute when transcribing into Latin
Read the rest over at mentalfloss here. Anyone up for a revival?
A useful update from the University of Michigan’s John Lawler:
Eth/Edh (ð) and ash (æ) are letters in the International Phonetic Alphabet, and also frequently-used phonemic symbols for English. Thorn never made it, however — the IPA and English phonemic symbol for voiceless interdental fricative is Greek theta (θ); ð is voiced, θ is voiceless. In most Middle English dialects, there was little or no phonemic distinction between voiced and voiceless TH; this was true of fricatives in general. But a multitude of changes brought distinctions between /s/ and /z/, /f/ and /v/, and inevitably /θ/ and /ð/. Though there are only two known minimal pairs for the /θ/-/ð/ distinction: ether (θ) vs either (ð), and thigh θ) vs thy (ð). This means that there’s very little “functional load” in the distinction, and that’s why we can get away with spelling them both the same way. Most people don’t even notice such differences until they collide with something.