This is the 1661st most frequent Polish word.
piekarnika
"Piekarnika" means "of the oven" or "oven’s" in English, showing possession.
Here, "piekarnika" is used in its possessive/genitive form to denote something belonging to the oven — specifically, the tray intended for use in the oven.
Muszę kupić nową blachę do piekarnika.
I need to buy a new tray for the oven.
In this sentence, "piekarnika" is in the accusative case, indicating the object being affected — the oven being touched (or warned against touching).
Nie dotykaj piekarnika, bo jest gorący.
Do not touch the oven because it is hot.
"Piekarnika" here is employed in the genitive to describe the subject, the oven's smell, portraying possession or origin.