Stem

The basic part of a verb is its "stem." This is the part that tends not to change and that carries the basic meaning of the verb. What would you think is the stem of ἀκούω?

1 sg
ἀκούω
I hear
2 sg
ἀκούεις
You hear
3 sg
ἀκούει
He/she/it hears

1 pl
ἀκούομεν
We hear
2 pl
ἀκούετε
Y'all hear
3 pl
ἀκούουσι
They hear

Right. I am sure you said, "ἀκου." (When listing the stem, you can ignore the accent but not the breathing mark.)

Important: if you compare this paradigm to the one for εἰμί, you will see a significant difference. In the case of εἰμί, the actual stems changes quite a bit. In the case of ἀκούω, the stem does not change at all. Most Greek verbs are like ἀκούω in that their stems do not change.