Borrowed from Ancient Greek κομήτης (komḗtēs, “long-haired; comet”), from κομᾰ́ω (komắō, “I have long hair”) + -της (-tēs, “-er”), the former from κόμη (kómē, “hair”) which itself was borrowed into Latin as coma.
Practice speaking and memorizing "cometes" and many other words and sentences in Latin.