This is the 2310th most frequent Turkish word.
dersi
"Dersi" means "the lesson" or "the class" in English.
In this sentence, 'dersi' refers to the lesson as the direct object of the verb 'listening'.
Dersi dikkatlice dinlememiz gerekiyor.
We need to listen to the lesson carefully.
Here, 'dersi' again refers to the lesson, this time as something that was taken at a specific time.
Dersi sabah saatlerinde almıştık.
We had taken the lesson during the morning hours.
In this case, 'dersi' indicates the lesson as the entity being finished, directly linked to the verb in the sentence.