An chéaddara litir den aibítir [[Ogham|oghaim]] is ea '''Luis''', ainmnithe as an gcrann, [[luis]]. Is é {{IPA|[l]}} a luach foghraíochta.
'' '''Luis''' () is the second letter of the [[Ogham]] alphabet, derived either from ''luise'' "[[fire|flame]]" or from ''lus'' "[[herb]]". Its [[Proto-Indo-European language|Proto-Indo-European]] root was either *''leuk-'' 'to shine' or *''leudh-'' 'to grow'. Its phonetic value is [l].<ref>{{cite book | title=A Guide to Ogam | last= McManus |first = Damian | year = 1991 | series = Maynooth Monographs | volume =4 | isbn= 1-870684-75-3 | issn = 0790-8806 | publisher = An Sagart | location = Co. Kildare, Ireland |page =36 | quote= The [[kennings]] point to an association of this letter name with either ''luise/loise'' 'flame, blaze' or ''lus'' 'plant, herb'. The word itself is not reliably attested in a context which would indicate its precise primary meaning but it is clearly related either to the root ''*leuk-'' 'to shine' or ''*leudh-'' 'to grow', either confirming /l/ as the value.}}</ref>
''The ''[[Auraicept na n-Éces]]'' glosses the name as ''cairtheand'' "mountain-ash", i.e. "[[rowan]]" (Modern Irish ''caorthann''). The associated verse is : ''Li sula'' "lustre of eye"
The Auraincept interprets this as "delightful to the eye is ''luis'', i.e. rowan, owing to the beauty of its berries".
