This is the 11788th most frequent Turkish word.
gelmediğini
"Gelmediğini" means "that (he/she/it) did not come."
Here, 'gelmediğini' is used in the clause 'he/she didn't attend', functioning within indirect speech to relate what others have said about someone not attending.
O toplantıya gelmediğini söylediler.
They said that he/she didn't attend the meeting.
In this sentence, 'gelmediğini' expresses a subordinate reason clause, elaborating on the assumed reason for someone's absence.
Havanın kötü olduğu için gelmediğini düşündüm.
I thought he/she didn't come because the weather was bad.
Here, 'gelmediğini' refers to something (an object or information) that presumably didn’t arrive to another person.