PIE pronominal stem, also root of Latin is, ea, id ‘he, she, it’ and item ‘also, likewise, in like manner’. See also *oi-no- ’one, unique’.
Other derivatives include item, iterate, ilk, yet, yonder, beyond.
[Pokorny *e-3, ei-, i-, fem. ī-, pp. 281–286 (demonstrative particle: one, this, etc.).]