This is the 198th most frequent Lithuanian word.
penktadienį
"Penktadienį" means "on Friday" in English.
In this sentence, 'penktadienį' in the accusative case is used to question the occurrence of an event (having a class) on the day 'Friday'.
Ar penktadienį turime pamoką?
Do we have a class on Friday?
Here, 'penktadienį' is once again in the accusative case and signifies a recurring action (working) that takes place on Fridays.
Aš dirbu kiekvieną penktadienį.
I work every Friday.
The word 'penktadienį' here indicates a specific day, 'Friday', on which the action 'einu į kiną' (going to the cinema) is taking place. It is in the accusative case, often used to specify a time when something happens.