This is the 13151st most frequent Polish word.
ogniem
"Ogniem" means "with fire" or "by fire" in English.
In this sentence, 'ogniem' represents the element of fire as the direct object of warming.
Ogrzaliśmy się przy ognisku pełnym ognia.
We warmed ourselves by the bonfire full of fire.
Here, 'ognistym' (adjective form) metaphorically describes the passion of the artist.
Artysta malował ognistym temperamentem.
The artist was painting with fiery temperament.
In this sentence, 'ognia' (genicive case) implies the specific source of fire.