As any grade-schooler can tell you, the alphabet we’re using right now is made up of 26 letters. However, until not too long ago, this cast of letters had a few more characters that have since been killed off, quashed, or exiled into oblivion.
The writing system used for modern English, along with many other European languages, is widely known as the Latin alphabet as it’s the great-grandchild of the classical Latin alphabet spread across much of Europe by the Romans.
However, like all writing systems, it’s history is complex and muddled with a whole load of interconnected influences from the past. The alphabet of Old English – the predecessor of modern English used in the early Middle Ages – also contained a number of letters that were derived from old regional dialects, Runic alphabets, the Gothic language, and Old Norse. The "Latinization" of the language did a good job at standardizing the alphabet across ancient Europe, but a small handful of these relics managed to sneak their way into some forms of the English written language until just 100 years ago.
Thorn (Þ, þ)
One of the letters derived from Runic alphabets was a letter called Thorn (Þ, þ), used to express the sound “th” makes in words such as "the" and “this.” It's still used in the modern Icelandic writing system, which has close links to Old Norse.
Thorn is the reason why some old-timey sentences that read stuff like: “Ye Olde Tavern.” In these cases, the "ye" is not pronounced with a "y" sound as we see it today; it was actually pronounced with a "th" sound. Since many of the printing presses at the time were imported from Germany and Italy, however, they didn't have a Thorn letter, so they simply used a "y" instead.
Eth (ð) is another letter used in Old English that has a similar story to Thorn. It was generally used to express the slightly longer “th” sound with a slight hint of a "d", a bit like the beginning of “thought” or “thump.” It isn’t clear why the letter fell out of favor, although scribes stopped using it towards the end of the Middle Ages.
You may have seen the letter Ash (æ) before; it was sometimes used in the early 20th century for names like “Cæsar,” though more recently it's come under legal scrutiny as part of Elon Musk's unusual baby name. It’s an Old English letter that’s used to represent a sound between an “a” and “e,” like the short "a" sound in words like "cat.”
Just like some of these other old letters, like Thorn, this letter is still used in modern-day Icelandic and Danish, although it’s used to represent a slightly different sound.
Insular G (ᵹ)
Originally an Irish letter, Insuglar G (Ᵹ) was used for throaty “ogh” sounds, like “cough” or “tough,” as opposed to hard “g” sounds like “frog” or “good.” This letter itself was derived from another old letter spoken in Middle English and Older Scots known as yogh (ȝogh or ȝ).
As you can probably guess just by looking at it, ethel (œ) was a smashing together of o and e. It was used to represent a short “e” sound. Although it's still occasionally used systemically in the words like "fœtus" or "amœba" in Britain, the conjoined letters have since been "separated" and simply replaced by the letter "e" in the US.
Wynn or wyn (Ƿ ƿ)
This a letter of the Old English alphabet used to represent the sound “uu.” It fell out of favor when the alphabet evolved into combining two u's to make our current letter “W.”