In the ancient Greek calendar, there were two types of months, "hollow" months that had 29 days, and "full" months which had 30 days. In latin, these were pleni mensis, "full" month, and cavi mensis as "hollow" month. In my search, I've found koílos mín (κοῖλος μήν) which means "hollow" month, and the term holóklēros (ὁλόκληρος) which means complete in all parts. So holóklēros mín should mean "full" month, but I can't find anything to corroborate this. If anyone knows the correct term I would be very grateful to learn it.
According to the extant writings of Geminos of Rhodes (Γεμῖνος, 1st century BC)
Ὅθεν διὰ ταύτην τὴν αἰτίαν οἱ κατὰ πόλιν μῆνες ἐναλλὰξ ἄγονται πλήρεις καὶ κοῖλοι
Ὅθεν κοῖλον καὶ πλήρη μῆνα παρὰ μέρος ἄγουσιν
Source: Patrologiae cursus completus, 801Α and 809A containing the original work 'Introduction to the Phenomena' / 'Εἰσαγωγή εἰς τὰ Φαινόμενα' (the above can be found elsewhere too, but the Patrologiae has the added benefit that it also provides a Latin translation with the Latin terms -pleni/cavi mensis- mentioned in your question)
So a full month would be a πλήρης μήν; as for Ὁλόκληρος or even Ὅλος, these should be plausible.
Excellent answer! I couldn't have asked for a better explanation. Thank you.– WalterSep 6, 2022 at 14:49