According to the High Medieval Bríatharogam, names of various trees can be ascribed to individual letters.
The earliest inscriptions in ogham date to about the 4th century AD, although the use of “classical” ogham in stone inscriptions seems to have flowered in the 5th and 6th centuries around the Irish Sea From the phonological evidence it is clear that the alphabet predates the 5th century. It appears that the ogham alphabet was modelled on another script, and some even consider it a mere cipher of its template script
In Ireland and in Wales, the language of the monumental stone inscriptions is termed Primitive Irish. The transition to Old Irish, the language of the earliest sources in the Latin alphabet, takes place in about the 6th century. Since ogham inscriptions consist almost exclusively of personal names and marks possibly indicating land ownership, linguistic information that may be glimpsed from the Primitive Irish period is mostly restricted to phonological developments.
The ogham alphabet originally consisted of twenty distinct characters (feda), arranged in four series aicmí (plural of aicme ). Each aicme was named after its first character (Aicme Beithe, Aicme hÚatha, Aicme Muine, Aicme Ailme, “the B Group”, “the H Group”, “the M Group”, “the A Group”). Five additional letters were later introduced (mainly in the manuscript tradition), the so-called forfeda.
The four primary aicmí are, with their transcriptions in manuscript tradition and their names according to manuscript tradition in normalised Old Irish, followed by their Primitive Irish sound values, and their presumed original name in Primitive Irish in cases where the name’s etymology is known.
- Right side/downward strokes
- B beith [b] (*betwi-s)
- L luis [l] (*lubsti-)
- F fearn [w] (*wernā)
- S saille [s] (*salik-s)
- N nuin [n]
- Left side/upward strokes
- H úath [j] (*osato-)
- D duir [d] (*darek-s)
- T tinne [t]
- C coll [k] (*koslas)
- Q ceirt [kʷ] (*kʷer[x]tā)
- Across/pendicular strokes
- M muin [m]
- G gort [ɡ] (*gorto-s)
- NG gétal [ɡʷ] (*gʷēdtlo-)
- Z straif [sw] or [ts]?
- R ruis [r] (*rudsti-)
- notches (vowels)
- A ailm [a]
- O onn [o] (*osno-)
- U úr [u]
- E edad [e]
- I idad [i]
- Beith, Old Irish Beithe means “birch-tree”.
- Luis, Old Irish Luis is either related to luise “blaze” or lus “herb”. The arboreal tradition has caertheand “rowan”.
- Fearn, Old Irish Fern means “alder-tree”, Primitive Irish *wernā, so that the original value of the letter was [w].
- Sail, Old Irish Sail means “willow-tree”.
- Nion, Old Irish Nin means either “fork” or “loft”. The arboreal tradition has uinnius “ash-tree”.
- Uath, Old Irish Úath means úath “horror, fear”, the arboreal tradition has “white-thorn”.
- Dair, Old Irish Dair means “oak” .
- Tinne, Old Irish Tinne from the evidence of the kennings means “bar of metal, ingot”. The arboreal tradition has cuileand “holly”.
- Coll, Old Irish Coll meant “hazel-tree”.
- Ceirt, Old Irish Cert is cognate with Welsh perth “bush”. It was confused with Old Irish ceirt “rag”, reflected in the kennings. The Auraicept glosses aball “apple”.
- Muin, Old Irish Muin: the kennings connect this name to three different words, muin “neck, upper part of the back”, muin “wile, ruse”, and muin “love, esteem”. The arboreal tradition has finemhain “vine”.
- Gort, Old Irish Gort means “field” (cognate to garden). The arboreal tradition has edind “ivy”.
- nGéadal, Old Irish Gétal from the kennings has a meaning of “killing”. The arboreal tradition glosses cilcach, “broom” or “fern”.
- Straif, Old Irish Straiph means “sulphur”. The arboreal tradition glosses draighin “blackthorn”.
- Ruis, Old Irish Ruis means “red” or “redness”, glossed as trom “elder”.
- Ailm, Old Irish Ailm is of uncertain meaning, possibly “pine-tree”. The Auraicept has crand giuis .i. ochtach, “fir-tree” or “pinetree”.
- Onn, Old Irish Onn means “ash-tree”, although the Auraicept glosses aiten “furze”.
- Úr, Old Irish Úr, based on the kennings, means “earth, clay, soil”. The Auraicept glosses fraech “heath”.
- Eadhadh, Old Irish Edad of unknown meaning. The Auraicept glosses crand fir no crithach “test-tree or aspen”
- Iodhadh, Old Irish Idad is of uncertain meaning, but is probably a form of ibhar “yew”, which is the meaning given to it in the arboreal tradition.
Of the forfeda, four are glossed by the Auraicept:
- Eabhadh, Old Irish Ebhadh with crithach “aspen”;
- Ór, “gold” (from Latin aurum); the arboreal tradition has feorus no edind, “spindle tree or ivy”
- Uilleann, Old Irish Uilleand “elbow”; the arboreal tradition has edleand “honeysuckle”
- Pín, later Ifín, Old Irish Iphin with spinan no ispin “gooseberry or thorn”.
- The fifth letter is Emancholl which means ‘twin of hazel’
The main use of ogham by modern Druids is for the purpose of divination. Divination by using ogham symbols is mentioned in Tochmarc Étaíne, a tale in the Irish Mythological Cycle. In the story, druid Dalan takes four wands of yew, and writes ogham letters upon them. Then he uses the tools for divination. The tale doesn’t explain further how the sticks are handled or interpreted. Another method requires a cloth marked out with Finn’s Window.
The divinatory meanings are usually based on the tree ogham, rather than the kennings of the Bríatharogam.