The reason why I would say I think it is a letter, is because it can be a letter in a root. Like in قرأ, the letter Alif is not considered the third letter in the verb, hamza is. I had to look it up, the grammatical term for it is الفعل المهموز, and all of the examples I can find have it placed on the alif in the root form, but it changes depending on how you conjugate it.
Also, what about the word for "thing" شيء it's not placed on the yaa, but written by itself. Or the plural form, things: أشياء has two hamzas in it, only one sits atop an alif.
Also, what about the word for "thing" شيء it's not placed on the yaa, but written by itself. Or the plural form, things: أشياء has two hamzas in it, only one sits atop an alif.
So that's a thing.