-ειν

Ancient Greek Etymology Seen in thematic verbs it may be from grc grk-pro *-ehen, from grc ine-pro *-os *-esen, locative case of action noun. Similar to la -ere (< ine-pro *-esi). See also grc -εναι, grc -έμεν, grc -μεναι. Pronunciation ειν Suffix grc suffix infinitive forming suffix References https://brill.com/view/journals/ieul/5/1/article-p49_3.xml#d1746598e246