ei- / Indo-European roots
Examples of words with the root ei-: adit, ambient, anion, cation, circuit, coitus, comitia, commence, concomitant, constable, count, county, dysprosium, errant, exit, eyre, Hinayana, initial, initiate, introit, ion, issue, itinerant, itinerary, janitor, January, Janus, Mahayana, obituary, perish.
To go.Oldest form *h1ei-, zero-grade *h1i-.
▲ Derivatives include ambition, perish, sudden, transit, ion, initial, janitor, January.
1. Full-grade form *ei-.
a. adit, ambient, ambition, circuit, coitus, comitia, exit, introit, issue, obituary, perish, praetor, preterite, sedition, subito, sudden, trance, transient, transit, transitive from Latin īre, to go;
b. ion; anion, cation, dysprosium from Greek ienai, to go;
c. Ramayana from Sanskrit eti, he goes (< Indo-Iranian *ai-ti), and abstract noun ayanam, a going, way.
2. Suffixed zero-grade form *i-t-.
a. Further suffixed form *i-t-yo-. commence, initial, initiate from Latin initium, entrance, beginning (in-, in; see en).
a. count2, county; concomitant, constable, viscount from Latin comes (stem comit-), companion (< "one who goes with another"; com-, with; see kom).
4. Suffixed form *i-ter. errant, eyre, itinerant, itinerary from Latin iter, journey.
5. Perhaps suffixed form *i-ti-. Gastarbeiter from Old High German arabeiti, labor, from Germanic *arbaithi- (see orbh-)
6. Extended form *yā- (< *h1yah2-, colored from earlier *h1yeh2-) in suffixed forms *yā-no-, *yā-nu-.
a. janitor, January, Janus from Latin iānus, archway, and Iānus, god of doors and of the beginning of a year;
b. Hinayana, Mahayana from Sanskrit yānam, way (in Buddhism, "mode of knowledge" "vehicle").
[Pokorny 1. ei- 293.]