Where does “καλοκαιρινός” come from?

καλοκαιρινός (Greek) comes from Greek καλοκαίρι, from Byzantine Greek καλοκαίριν, from Ancient Greek καλοκαίριον — fine weather.

καλοκαιρινός (Greek): summery, summer, summer-; 'see vernacular...

Definitions

Step	Language	Word	Meaning
1	Greek	καλοκαίρι	summertime, summer
2	Byzantine Greek	καλοκαίριν	good season, good weather
3	Ancient Greek	καλοκαίριον	fine weather