[talideon]

It's cognate with 'deich/déag' in Irish and 'deg' in Welsh, both of which mean 'ten', which is an interesting artifact, and likely down to 'dau ddeg' being one of the ways in Welsh of saying 'twenty', but that's a relatively recent change from influence from English and other languages, as the various Celtic languages are traditionally base-20. You can see some echoes of this in French to this day, as it inherited its manner of counting from Gaulish.