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Theforfeda (sing.forfid) are the "additional" letters of theOgham alphabet, beyond the basic inventory of twenty signs. Their name derives fromfid ("wood", a term also used for Ogham letters) and the prefixfor- ("additional").^[1][2][3] The most important of these are fiveforfeda which were arranged in their ownaicme or class, and were invented in theOld Irish period, several centuries after the peak of Ogham usage. They appear to have represented sounds felt to be missing from the original alphabet, maybeé(o),ó(i),ú(i),p andch.^{[clarification needed]}

The five "aicme"forfeda are glossed in the manuscriptsAuraicept na n-Éces ('The Scholars' Primer),De dúilib feda ('Elements of the Letters') andIn Lebor Ogaim ('The Book of Ogam'), by severalBríatharogaim ("word oghams"), or two wordkennings, which explain the meanings of the names of the letters of theOgham alphabet.Theforfeda letter names and their kennings, as edited (in normalized Old Irish) and translated by McManus (1988), are as follows:

Four of these names are glossed in the Auraicept with tree names,ebad ascrithach "aspen",oir asfeorus no edind "spindle-tree orivy",uilleand asedleand "honeysuckle", andiphin asspinan no ispin "gooseberry orthorn".

The kennings forÉabhadh point to the soundéo oré, which is also the word for "salmon". The name appears modelled afterEadhadh andIodhadh. The kennings forÓr point to the wordór "gold" (cognate to Latinaurum). The kenning ofUilleann, "great elbow", refers to the letter name. Since the Ogham alphabet dates to thePrimitive Irish period, it had no sign for[p] in its original form and the letterPín was added as a letter to express it. McManus states that the namePín was probably influenced by Latinpinus ('pine'), but a more likely explanation is that it derives from Latinspina ('thorn'), as the kennings indicate a tree or shrub with sweet tasting fruit (therefore not a pine). According to Kelly (1976) the namespín (deriving from the Latin) appears in the Old Irish tree lists as meaning either gooseberry or thorn, so the medieval glosses may be correct on this occasion. The nameEamhancholl means "twinnedcoll", referring to the shape of the letter (ᚙ resembling two ᚉ), and also perhaps referring to its sound being similar to that ofcoll ([x] being africative variant of[k]). The Bríatharogam kenning "groan of a sick person" refers to a valuech[x], predating the decision that all fiveforfeda represent vowels.

Apart from the first letter, theforfeda were little used in inscriptions, and this led later oghamists to rearrange them as a series of vowel diphthongs, necessitating a complete change to the sounds ofPín andEamhancholl (the namePín also had to be changed toIphín). This arrangement is how they appear in most manuscripts:

• ᚕ (U+1695)Éabhadh:ea,éoea;
• ᚖ (U+1696)Ór:oióe,oi;
• ᚗ (U+1697)Uilleann:ui,úa,ui;
• ᚘ (U+1698)Ifín:io,ía,ia;
• ᚙ (U+1699)Eamhancholl:ae.

This arrangement meant that once again the ogham alphabet was without a letter for the[p] sound, making necessary the creation ofPeith (see below).

Apart from the first letterÉabhadh, theforfeda do not appear often in orthodoxogham inscriptions.Éabhadh was in fact frequently used as part of the formula wordKOIᚕᚑᚔ, but with the value/k/ or/x/. KOI means something like 'here' and is the ogham equivalent of the Latinhic iacet (McManus §5.3, 1991); it is etymologically linked with the Latincis ("on this side"). It also appears with its vocalic value in later orthodox inscriptions however. Of the otherforfeda the next three appear only a few times, and the last letterEamhancholl does not appear at all. So rare are the otherforfeda in inscriptions that it is worthwhile detailing the individual examples (numbering as given by Macalister):

• Óir appears twice:

• In an inscription in Killogrone in County Kerry (235), which reads:

• In a late inscription on a cross slab at Formaston in Aberdeenshire, which reads:

• Uilleann appears only once, in an inscription in Teeromoyle, again in County Kerry (240). The inscription reads:

• Pín appears in two, or possibly three, inscriptions.

• In Cool East on Valencia Island in County Kerry (231), which reads:

The letter[p] appears as an X shape instead of the 'double X' shape of the letter, presumably because the correct letter shape is quite hard to carve.

• In Crickowel in Breconshire in Wales (327) which reads:

Again an X shape is used.

• In Margam in Glamorganshire in Wales (409) which reads:

However, much of the inscription is broken off and what remains looks like a squat arrowhead. It almost certainly stands for[p] however, as the ogham inscription is accompanied by one in Latin which confirms the sound.

Beyond the fiveforfeda discussed above, which doubtlessly date toOld Irish times, there is a large number of letter variants and symbols, partly found in manuscripts, and partly in "scholastic" (post 6th century) inscriptions collectively termedforfeda. They may date toOld Irish,Middle Irish or even early modern times.

Due to the "schematicism of later Ogamists" (McManus 1988:167), who insisted on treating the five primary forfeda as vowels,[p] had again to be expressed as a modification of[b], calledpeithe, afterbeithe, also calledbeithe bog "softbeithe" or, tautologically,peithbog (ᚚPeith, Unicode allocation U+169A).

The 7th-12th centuryAuraicept na n-Éces among the 92 "variants" of the Ogham script gives more letters identified asforfeda (variant nrs. 79, 80 and 81).

The Bressay stone inShetland (CISP BREAY/1) contains five forfeda, three of them paralleled on other Scottish monuments and also in Irish manuscripts, and two unique to Bressay. One of the latter is possibly a correction of an error in carving and not intended as a forfid. One is "rabbit-eared", interpreted as some kind of modified D, presumably the voiced spirant. Another is an "angled vowel", presumably a modified A. One unique character consists of five undulating strokes sloping backwards across the stem, possibly a modified I. The fourth is a four-stroke cross-hatching, also appearing in the late eighth or ninth-century Bern ogham alphabet and syllabary under a label which has previously been read as RR, but another suggestions is SS. It appears in theBook of Ballymote, scale no. 64.CISP - BREAY/1

• Kelly, Fergus 'The Old Irish Tree-list'Celtica 11 (1976) pp122–3
• Macalister, Robert A.S.Corpus inscriptionum insularum celticarum. First edition. Dublin: Stationery Office, 1945–1949. OCLC 71392234
• McManus, Damian.Ogam: Archaizing, Orthography and the Authenticity of the Manuscript Key to the Alphabet, Ériu 37, 1988, 1-31. Dublin: Royal Irish Academy. OCLC 56088345
• McManus, DamianIrish letter-names and their kennings, Ériu 39 (1988), 127–168.
• McManus, Damian.A Guide to Ogam, Maynooth 1991.ISBN 1-870684-17-6 OCLC 24181838
• Sims-Williams, PThe additional letters of the Ogam Alphabet, Cambridge Medieval Celtic Studies, 23: 29-75 (1992).

• The Ogam Scales from the Book of Ballymote by B. Fell

• Ogham letters

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