The proper latinized form of the Greek given name Achaikos is actually Achaecus, not Achaicus. After all, -ai- in Greek becomes -ae- in Latin. There are several examples of this in the main database, such as:- Alkaios becomes Alcaeus in Latin; - Daidalos becomes Daedalus in Latin; - Eirenaios becomes Irenaeus in Latin; - Hephaistos becomes Hephaestus in Latin; - Phaidros becomes Phaedrus in Latin; - Timaios becomes Timaeus in Latin.So, it seems to me that Achaicus is a semi-latinized form at best.Also, a variant form of Achaikos is Achaiikos (also variantly spelled as Akhaiikos), which is latinized to Achaeicus.- https://lsj.translatum.gr/w/index.php?title=%E1%BC%88%CF%87%CE%B1%CE%B9%CE%B9%CE%BA%CF%8C%CF%82 (in English).
- Alkaios becomes Alcaeus in Latin;
- Daidalos becomes Daedalus in Latin;
- Eirenaios becomes Irenaeus in Latin;
- Hephaistos becomes Hephaestus in Latin;
- Phaidros becomes Phaedrus in Latin;
- Timaios becomes Timaeus in Latin.
So, it seems to me that Achaicus is a semi-latinized form at best.
Also, a variant form of Achaikos is Achaiikos (also variantly spelled as Akhaiikos), which is latinized to Achaeicus.
- https://lsj.translatum.gr/w/index.php?title=%E1%BC%88%CF%87%CE%B1%CE%B9%CE%B9%CE%BA%CF%8C%CF%82 (in English).