Worm, wurm or wyrm (Old English: wyrm; Old Norse: ormr; Old High German: wurm), meaning serpent, are archaic terms for dragons (Old English: draca; Old Norse: dreki/*draki; Old High German: trahho) in the wider Germanic mythology and folklore, in which they are often portrayed as large venomous snakes and hoarders of gold. Especially in later tales, however, they share many common features with other dragons in European mythology, such as having wings.

Prominent worms attested in medieval Germanic works include the dragon that killed Beowulf, the central dragon in the Völsung Cycle – Fáfnir, Níðhöggr, and the great sea serpent, Jǫrmungandr, including subcategories such as lindworms and sea serpents.

In early depictions, as with dragons in other cultures (compare Russian: zmei), the distinction between Germanic dragons and regular snakes is blurred, with both being referred to as: "worm" (Old English: wyrm, Old Norse: ormʀ → ormr, Old High German: wurm), "snake" (Old English: snaca, Old Norse: snókr, snákr, Old High German: *snako), "adder" (Old English: nǣdre, Old Norse: naðr, Old High German: nātara), and more, in writing; all being old Germanic synonyms for serpent and thereof (compare the names for the common legless lizard: blindworm, hazelworm, slowworm, deaf adder etc).

The descendent term worm remains used in modern English to refer to dragons, such as those similar to snakes or without wings, while the Old English form wyrm has been borrowed back into modern English to mean "dragon". The Nordic descendants of Old Norse: ormr – Danish: orm, Faroese: ormur, Icelandic: ormur, Norwegian: orm, Swedish: orm – beyond being the common word for snake in Faroese, Norwegian and Swedish, in Danish and Icelandic instead being more ambiguous with invertebrate worms, remain a poetic or archaic word for dragon and similar mythological serpentine creatures. A similar theme can be seen in German, with surviving compositions such as Lindwurm and Tatzelwurm etc.

The word "dragon", contemporaneously also appear: Old English: draca, dræce; Old West Norse: dreki, Old East Norse: *draki; Old Swedish: draki; Old Danish: draghæ; Old High German: trahho, tracho, tracko, trakko; Middle High German: trache; Old Saxon: *drako; Middle Low German: drāke, meaning "dragon, sea serpent or sea monster" etc, stemming from Latin: dracō, meaning "big serpent or dragon", itself from Ancient Greek: δράκων (drákōn) of the same meaning.

The Old West and East Norse forms differ quite remarkebly, as the Western form, dreki, features an initial e-vowel, largely unique among the Germanic forms, which otherwise feature an a-vowel, indicating an early adoption which then had time to shift, potentially from the Old English form dræce. Old Swedish, and Old Danish, both East Norse languages, instead exhibit forms on /a/: draki/draghæ, indicating a Central European root. When the term entered the East Norse language is unknown. The form "dragon", in modern English, stems from Old French: dragon, while the Germanic Old English form survives as drake.

A poem, by 11th-century Icelandic skáld Þjóðólfr Arnórsson, manages to use all four above mentioned terms in a single poem about Sigurd the dragon slayer, based on a fight between a blacksmith and a leather worker, which Arnórsson supposedly composed spontaneously upon request:

Sigurðr eggjaði sleggju / snák váligrar brákar, / en skafdreki skinna / skreið of leista heiði. / Menn sôusk orm, áðr ynni, / ilvegs búinn kilju, / nautaleðrs á naðri / neflangr konungr tangar.