This is the 11793rd most frequent Turkish word.
gelmeyen
"One who/that which does not come."
Here, "gelmeyen" refers to the bus as the subject that did not arrive, formed by adding the negative suffix "-me" and the adjectival participle suffix "-yen" to the verb stem "gel-". It functions as an adjective modifying "bus".
Gelmeyen otobüs yüzünden işe geç kaldım.
I was late for work because of the bus that didn't come.
In this sentence, "gelmeyen" is used to describe "letter" as the one that hasn't arrived yet, emphasizing its non-arrival with an ongoing sense.
Beklediğimiz mektup hâlâ gelmeyen oldu.
The letter we were expecting is still the one that hasn't come.
Here, "gelmeyen" describes "friend" as the subject who has not come, focusing on the person's absence.