This is the 7768th most frequent Russian word.
ильи
"Ильи" is the genitive singular or plural form of "Илья," a Russian male given name, meaning "of Ilya" or "Ilyas."
In this sentence, 'ильи' is in the genitive case, referring to possession or association with Ilya.
Ильи сегодня не было на уроке.
Ilya was not present at the lesson today.
Here, 'ильи' again is in the genitive case, showing possession related to Ilya.
Мы видели свет ильи горящей свечи.
We saw the light of Ilya's burning candle.
In this case, 'ильи' is used in the dative case, indicating the grammatical role of being the recipient.