Coll (letter) explained

Coll is the Irish name of the ninth letter of the Ogham alphabet ᚉ, meaning "hazel-tree", which is related to Welsh pl. , and Latin . Its Proto-Indo-European root was *kos(e)lo-. Its phonetic value is [k].^[1]

Bríatharogam

In the medieval kennings, called Bríatharogam or Word Ogham the verses associated with Coll are:

• caíniu fedaib – "fairest tree" in the Bríatharogam Morann mic Moín
• carae blóesc – "friend of nutshells" in the Bríatharogam Mac ind Óc
• milsem fedo – "sweetest tree" in the Bríatharogam Con Culainn.^[2]

References

1. Book: McManus, Damian . A Guide to Ogam . 1991 . Maynooth Monographs . 4 . 1-870684-75-3 . 0790-8806 . An Sagart . Co. Kildare, Ireland . 37 . The name of the ninth letter of the alphabet is the word for 'hazel-tree', Old Irish coll, cognate with Welsh collen pl. cyll hazel-tree(s), Latin corulus from the root *kos(e)lo-. The etymology confirms /k/ (as opposed to /kʶ/, see the next letter) as the value of this letter in Primitive Irish..
2. McManus. Damian. 1988. Irish Letter-Names and Their Kennings. Ériu. 39. 127–168. 30024135.