or Ch (as in loch), later AE emancholl ; Letter names The letter names are interpreted as names of trees or shrubs in manuscript tradition, both in Auraicept na n-Éces ('The Scholars' Primer') and In Lebor Ogaim ('The Ogam Tract'). They were first discussed in modern times by Ruaidhrí Ó Flaithbheartaigh (1685), who took them at face value. The Auraicept itself is aware that not all names are known tree names: "Now all these are wood names such as are found in the Ogham Book of Woods, and are not derived from men", admitting that "some of these trees are not known today". The Auraicept gives a short phrase or kenning for each letter, known as a Bríatharogam, that traditionally accompanied each letter name, and a further gloss explaining their meanings and identifying the tree or plant linked to each letter. Only five of the twenty primary letters have tree names that the Auraicept considers comprehensible without further glosses, namely beith "birch", fearn "alder", saille "willow", duir "oak" and coll "hazel". All the other names have to be glossed or "translated". According to the leading modern ogham scholar, Damian McManus, the "Tree Alphabet" idea dates to the Old Irish period (say, 10th century), but it postdates the Primitive Irish period, or at least the time when the letters were originally named. Its origin is probably due to the letters themselves being called feda "trees", or nin "forking branches" due to their shape. Since a few of the letters were, in fact, named after trees, the interpretation arose that they were called feda because of that. Some of the other letter names had fallen out of use as independent words, and were thus free to be claimed as "Old Gaelic" tree names, while others (such as ruis, úath or gort) were more or less forcefully reinterpreted as epithets of trees by the medieval glossators. McManus (1991, §3.15) discusses possible etymologies of all the letter names, and as well as the five mentioned above, he adds one other definite tree name: onn "ash" (the Auraicept wrongly has "furze"). McManus (1988, p. 164) also believes that the name Idad is probably an artificial form of Iubhar "yew", as the kennings support that meaning, and concedes that Ailm may possibly mean "pine tree," as it appears to be used to mean that in an 8th-century poem. Thus out of twenty letter names, only eight