This is the 427th most frequent Hebrew word.
עלינו
"Upon us" or "it is incumbent upon us."
Here, 'עלינו' conveys obligation or necessity.
עלינו ללמוד בכל יום.
We must study every day.
In this case, 'עלינו' refers to something being physically above or over us.
המטוס טס מעלינו בגובה רב.
The plane flew above us at a great height.
Again, 'עלינו' indicates responsibility or a required action.