From Irish Names and Surnames 1923
CÁRTHACH, genitive -aigh, Cartagh, Carthage; Old Irish — Carthach, from Celt. *karatako-s, loving; an ancient Irish name borne by the celebrated Abbot and Bishop of Lismore and patron of that diocese. Latin — Carthachus, Carthagus.
Alphabetical Index to Names of Men (Irish-English)
Note: The old Irish letters used in the original text* have been converted to the Roman alphabet for this online version, and the lenited (or dotted) consonants changed to their aspirated equivalents, i.e. the dotted 'c' has been altered to 'ch', the dotted 'g' to 'gh', and the dotted 'm' to 'mh', etc. For example, in the name Caoimgin (Kevin), where the 'm' and 'g' are both dotted (ṁ, ġ) in the old Irish lettering, the name has been converted here to the modern Irish equivalent of Caoimhghin.
* Sloinnte Gaedheal is Gall: Irish Names and Surnames by Rev. Patrick Woulfe, 1923.