Where does “plág” come from?

plág (Old Irish) comes from Latin plāga, from Latin plagius, from Ancient Greek πλάγιος, from Ancient Greek -ῐος, from Proto-Indo-European -yós — Creates adjectives from noun or verb stems.

Ancestry of “plág”, step by step

Step	Language	Word	Meaning
1	Latin	plāga	plague, misfortune
2	Latin	plagius	—
3	Ancient Greek	πλάγιος	placed sideways, slanting, aslant
4	Ancient Greek	-ῐος	belonging to; of”, “belonging to”, “pertaining to
5	Proto-Indo-European	-yós	Creates adjectives from noun or verb stems

Every word from Proto-Indo-European -yós →Every word from Ancient Greek -ῐος →Every word from Ancient Greek πλάγιος →