Ogham

Borrowed from Irish ogham, from Middle Irish ogam, from Proto-Celtic *ogmos (“furrow, path”), from Proto-Indo-European *h₂óǵmos. The Irish word is frequently folk-etymologized as og-úaim, referring to ogham being supposedly made by the point of a sharp weapon, but this approach faces serious phonological and morphological problems in that: * The name of ogham and the supposed second element (úaimm (“seam”)?) inflected very differently in Early Irish, "ogham" being an o-stem and the second element being a neuter n-stem. * Middle Irish ogmóir (“skilled in ogham”) should have a vowel in between the g and m because vowels lengthened by compensatory lengthening after consonant loss are usually not syncopated in Early Irish.

来源：wiktionary