The Old Norse word galdr is derived from a word for singing incantations, gala (Old High German and Old English: galan) with an Indo-European -tro suffix. In Old High German the -stro suffix produced galster instead.
The Old English forms were gealdor, galdor, ȝaldre "spell, enchantment, witchcraft", and the verb galan meant "sing, chant". It is contained in nightingale (from næcti-galæ), related to giellan, the verb ancestral to Modern English yell; cf. also the Icelandic verb að gala "to sing, call out, yell". In Dutch language gillen.
The German forms were Old High German galstar and MHG galster "song, enchantment" (Konrad von Ammenhausen Schachzabelbuch 167b), surviving in (obsolete or dialectal) Modern German Galsterei (witchcraft) and Galsterweib (witch).
The incantations were composed in a special meter named galdralag. This meter was similar to the six-lined ljóðaháttr but adds a seventh line. Another characteristic is a performed parallelism, see the stanza from Skirnismál, below.
A practical galdr for women was one that made childbirth easier, but they were also notably used for bringing madness onto another person, whence modern Swedish galen meaning "mad". Moreover, a master of the craft was also said to be able to raise storms, make distant ships sink, make swords blunt, make armour soft and decide victory or defeat in battles. Examples of this can be found in Grógaldr and in Frithiof's Saga. In Grógaldr, Gróa chants nine (a significant number in Norse mythology) galdrar to aid her son, and in Buslubœn, the schemes of king Ring of Östergötland are averted.
It is also mentioned in several of the poems in the Poetic Edda, and for instance in Hávamál, where Odin claims to know 18 galdrar. For instance, Odin mastered galdrar against fire, sword edges, arrows, fetters and storms, and he could conjure up the dead and speak to them. There are other references in Skírnismál, where Skirnir uses galdrar to force Gerðr to marry Freyr as exemplified by the following stanza:
A notable reference to the use of galdrar is the eddic poem Oddrúnargrátr, where Borgny could not give birth before Oddrún had chanted "biting galdrar" (but they are translated as potent charms, by Henry Adams Bellows below):
- The article Galder in Nationalencyklopedin (1992)
- Steinsland, G. & Meulengracht Sørensen 1998:72
- The article galder in Henrikson A., Törngren D. and Hansson L. (1998). Stora mythologiska uppslagsboken. ISBN 91-37-11346-1
- Hellquist, E. (1922). Svensk etymologisk ordbok. C. W. K. Gleerups förlag, Lund. p. 177
- The article Galdralag in Nationalencyklopedin (1992)
- The article galder in Nordisk familjebok (1908).
- Schön 2004:86
- Skírnismál at «Norrøne Tekster og Kvad», Norway.
- Skirnismol in translation by Henry Adams Bellows.
- Oddrúnarkviða at «Norrøne Tekster og Kvad», Norway.
- The Lament of Oddrun in Henry Adams Bellows' translation.
- Schön, Ebbe. (2004). Asa-Tors hammare, Gudar och jättar i tro och tradition. Fält & Hässler, Värnamo.
- Steinsland, G. & Meulengracht Sørensen, P. (1998): Människor och makter i vikingarnas värld. ISBN 91-7324-591-7