What does Thumn mean?
With two Athman (plural of Thumn) making up a Rub', this fine-grained division helps structure daily memorization or revision goals down to a very manageable amount of text.
Quran Structure
Thumn
ثمن: /ðʊmn/
A Thumn is one-eighth of a Hizb, one of the smallest standard divisions used to section the Quran.