There's no single perfect translation of "Minotaur" into Ancient Greek because it's a word from later mythology and not directly attested in ancient texts. However, you could construct a descriptive phrase that captures its meaning. The most common and accepted approach would be something like:
Μινώταυρος (Minōtauros)
This combines "Mīnos" (Μῖνος), referring to King Minos, and "tauros" (ταῦρος), meaning "bull." This is a highly plausible and widely used reconstruction. It directly translates the mythical creature's etymology.