Beith is the Irish name of the first letter of the Ogham alphabet, ᚁ, meaning "birch". In Old Irish, the letter name was Beithe, which is related to Welsh bedw(en), Breton bezv(enn), and Latin betula. Its Proto-Indo-European root was *gʷet- 'resin, gum'. Its phonetic value is [b].
|Aicme Beithe||Aicme Muine|
|Aicme hÚatha||Aicme Ailme|
|“||This moreover is the first thing that was written by Ogham, [illustration of seven b's, in Ogham script] i.e. (the birch) b was written, and to convey a warning to Lug son of Ethliu it was written respecting his wife lest she should be carried away from him into faeryland, to wit, seven b’s in one switch of birch: Thy wife will be seven times carried away from thee into faeryland or into another country, unless birch guard her.
On that account, moreover, b, birch, takes precedence, for it is in birch that Ogham was first written.
In the medieval kennings, the verses associated with Beith are:
- Féocos foltchaín: "Withered foot with fine hair" (Word Ogham of Morann mic Moín)
- Glaisem cnis: "Greyest of skin" (Word Ogham of Mac ind Óc)
- Maise malach: "Beauty of the eyebrow" (Word Ogham of Culainn)
Peith ᚚ, a late addition to the Forfeda, is a variant of Beith, with a phonetic value of [p], also called beithe bog "soft beithe", [p] being considered a "soft" variant of [b]. It likely replaced Ifín ᚘ, one of the "original" five Forfeda. Prior to the addition of the Forfeda to the original twenty letters, both [p] and [b] were probably symbolized by the same letter: Beith.