This is the 7236th most frequent Turkish word.
ertuşi
"Ertuşi" does not appear to be a standard Turkish word. It may be a proper noun, a regional term, or a misspelling.
Here, 'Ertuşi' is used as a proper noun referring to a person.
Ertuşi her zaman doğruyu söyleyen bir insandır.
Ertuşi is someone who always tells the truth.
In this sentence, 'Ertuşi' is again used as a proper noun, but the context is about discussing the origin of the name.
Ertuşi adını nereden aldı bilmiyorum.
I don't know where Ertuşi got his name from.
In this instance, 'Ertuşi' refers to a specific person whose past is being discussed in a narrative context.