Similar words
reja
reja is more for a security or window grille, iron bars; rejilla is more for a small grid or mesh, like a vent grille or drain grate.
Similar in other languages
Portuguese
grade
grade is the Portuguese word for the same thing — both mean "grille."
Practice
1 What does rejilla mean?
grille
2 Fill the gap: Coloca la ___.
Full sentence: Coloca la rejilla. (Put on the grille.)
3 Which fingerprint chart matches rejilla?
rejilla: neutral register, academic frequency, general domain, neutral connotation.