This is the 115th most frequent Vietnamese word.
thuộc
"Thuộc" means "belonging to," "related to," "pertaining to," or "memorize" depending on context.
Here, 'thuộc' means to memorize or to know something by heart.
Tôi thuộc bài thơ này.
I have memorized this poem.
In this usage, 'thuộc' is part of the phrase 'thuộc về', meaning 'to belong to'.
Nhà sách này thuộc về chúng tôi.
This bookstore belongs to us.
Here, 'thuộc' denotes classification or belonging in a scientific or categorization sense.