* διδασκαλία (didaskalia): This means "teaching" or "instruction" in a general sense. It's a good general term and likely the closest single word.
* φροντιστηριακή (frontistiriaki): This refers to "private tuition" or "supplementary instruction," often implying a more structured setting than just casual teaching. It's derived from φροντιστήριο (frontistirio), which means "private tutoring center" or "cram school."
* ιδιαίτερα μαθήματα (idiaitera mathēmata): This phrase translates to "private lessons" and is a very common way to refer to tutoring.
The best choice depends on the context. For general use, διδασκαλία is a good starting point. If you want to emphasize the private and structured nature of tutoring, φροντιστηριακή or ιδιαίτερα μαθήματα would be more appropriate.