This is the 16104th most frequent Turkish word.
vefatını
"Vefatını" means "his/her/its death."
Here, 'vefatını' refers to 'passing/death' as the object of the sentence, illustrating its connection with 'duyduğumda' as subject action.
Amcamın vefatını duyduğumda çok üzüldüm.
I was very saddened when I heard about my uncle's passing.
'Vefatını,' in this context, indicates 'passing' and is used to describe the event being commemorated, linked with 'anma töreni düzenledik' as there is a causal effect.
Onun vefatını anma töreni düzenledik.
We organized a memorial ceremony for his passing.
In this sentence, 'vefatını' functions as the subject specification wherein 'great poet's passing/death' is recognized by 'herkes biliyor'.