Analysis of information sources in references of the Wikipedia article "Coll (letter)" in English language version.
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.