Disputed. The initial -kur- is obviously Kurd, but theories vary on the -manc- part. Chyet considers it to be a modern Kurdish equivalent of Mede, this falls in line with Kurdish sound changes as in *Mād ("Mede") > *mānd (n-extension before d/t/č/c sounds; as in tanc, derence, fersend...) > mānc (as in gazind > dialectal gazinc); Kurd-Mede. However in Zand-i Wahman yasn, a Middle Persian text, the word /karmān/ is used together and synonymously with /kurd/, apparently connected to Kurmanc, Kerman and Kermanshah. Might originally be the name of a tribe.
kurmanc ?
While it is now only used by Kurds in Turkey, Syria and Caucasia; Kurmanc was the name of all speakers of the Kurdish languages and "Kurd" either referred to other Northwestern Iranic groups (Zaza, Hawrami, Shabaki etc.) or for noblemen. Plenty of Kurdish rebellious leaders historically expressed annoyance to the Ottomans lumping them in the same group as the Kurmanjs, and often considered settled Kurds to be gawir (infidel, pagan) and called them Goran (*gawiran; infidels, pagans). In some regions Kurmanc still refers to a fake or a lesser Kurd or a Kurd with no tribe. Nomadic Kurds mostly don't call themselves Kurmanc. Considering oneself as the "true Kurds" is common among Kurdish tribes and groups. Melayê Cizîrî uses Mîr û Kurmanc ("prince and Kurmanj) which shows that Kurmanj isn't a nobleman. This changed after the 19th century when the Kurdish noble classes dissappeared after the Ottomans ended Kurdish principalities. While presently only Northern Kurdish (called Badînanî by outsiders) is called Kurmanji, it only dissappeared after the 70s in the rest of Kurdistan and the speakers of other Kurdish languages did not call their variant "Soranî", "Palewanî", "Feylî", etc. It is now quite rare in Iraq and Iran and in much rarer forms such as kurdmanc, kirmanc, kumanc, etc.