What is the greek word for self?

The most common Greek word for "self" is ἑαυτοῦ (heautou), which is the genitive case of ἑαυτός (heautos). The form used depends on the grammatical context (nominative, genitive, etc.). There are other words that can convey the idea of self depending on the nuance, but heautou/heautos is the most direct and frequent translation.