Many people are aware of the link between wormwood and absinthe. As names for the plant Artemisia absinthium, they are synonyms. A. absinthium has been used for many centuries to add a bitter flavor to various concoctions, especially wines and liqueurs. It has even taken the place of hops in some beer recipes.
The cultural association of A. absinthium with bitterness—an unpalatably bitter flavor, even—is so old that the Greek name for this plant, ἄψινθος, shows up in the Book of Revelation as a metaphor for undrinkable water:
10Καὶ ὁ τρίτος ἄγγελος ἐσάλπισεν: καὶ ἔπεσεν ἐκ τοῦ οὐρανοῦ ἀστὴρ μέγας καιόμενος ὡς λαμπάς, καὶ ἔπεσεν ἐπὶ τὸ τρίτον τῶν ποταμῶν καὶ ἐπὶ τὰς πηγὰς τῶν ὑδάτων. 11καὶ τὸ ὄνομα τοῦ ἀστέρος λέγεται ὁ Ἄψινθος. καὶ ἐγένετο τὸ τρίτον τῶν ὑδάτων εἰς ἄψινθον, καὶ πολλοὶ τῶν ἀνθρώπων ἀπέθανον ἐκ τῶν ὑδάτων, ὅτι ἐπικράνθησαν. (Rev. 8:10–11)
10And the third angel trumpeted; and a great star fell out of the sky, burning like a torch; and it fell onto one-third of the rivers and onto the springs of the waters. 11And the name of the star is called Ápsinthos. And one-third of the waters turned to ápsinthon, and many people died from the waters, because they had been made bitter.
The name of the star, Ápsinthos, is usually translated as Wormwood in English Bibles, although there are a few that use Bitterness:
Wormwood—NAB, NASB, NIV, (N)KJV, (N)RSV
The modern English name for A. absinthium, wormwood, sounds like it has something to do with worms (perhaps because only worms should rightly consume such a bitter plant) and wood (it is a plant, after all). In fact, this is an example of folk etymology. The Old English source of this word is wermōd, which has nothing to do with either worms or wood. One generation of medieval English speakers simply misunderstood wermōd, imagining that what they were hearing was really a compound of worm+wood, and then changed the spelling to accommodate this notion.
Here is the entry for absintium in the Épinal-Erfurt glossary, a very early (late 7th century) Latin-to-Old English lexicon. The term is glossed as uuermod.
(Épinal, Bibliothèque Municipale MS 72, f. 1vcd, l. 66)
The original word, OE wermōd, is cognate with German Wermut, which refers to the same plant and has been used to translate ἄψινθος in Rev. 8:11 since Martin Luther’s 1522 translation of the New Testament.
(Wittenberg 1541—Coburg, Landesbibliothek P I 1/10)
Old English wermōd and German Wermut together point to West Germanic *wermōd, which itself is not elsewhere attested. At risk of imposing another folk etymology on the word, it is tempting to look at *wermōd as a compound of Proto-Germanic *weraz ‘man’ and *mōdaz ‘mind, sense, zeal’ (cf. mood).
The first element of this hypothetical compound is related to Latin vir and Irish fear ‘man,’ and is the otherwise obsolete first element of werewolf (lit. ‘man-wolf’).
The second element of reconstructed *wer-mōdaz would be the same word as German Mut ‘courage, valor,’ which originally refers to any kind of state of mind, and shows up in many compounds in the modern language—e.g. Anmut ‘grace,’ Demut ‘humility,’ Hochmut ‘pride,’ Übermut ‘haughtiness,’ Unmut ‘discontent,’ Wankelmut ‘fickleness.’
But the combination of ‘man’ + ‘mood’ referring to A. absinthium does seem like a stretch.
So, the name for the wormwood plant is straightforward, even if the pre-West Germanic etymology is somewhat opaque. But over the course of history, the Latin (originally Greek) absinthium was applied to a certain anise-flavored liqueur whose extended history I will not go into here. The drink that we call absinthe thus got its name in French from its signature ingredient, A. absinthium. English speakers—as often happens with foreign foods, drinks, and technologies—imported the French name along with the product.
However, the German Wermut underwent the same metonymic transformation as absinthe did in French, and so to a large degree any drink that contained A. absinthium was liable to be called Wermut. One such style of beverage that made its way into France—an aromatized and fortified wine frequently mixed into cocktails but also consumed on its own as an apéritif—acquired a name that is in fact nothing more than German Wermut ‘wormwood’ fitted into the phonological system of French: vermouth.