This is the 255th most frequent Vietnamese word.
du
"Du" in Vietnamese means "to travel" or "tourism."
Here, 'đủ' refers to the sufficiency of money, showing its adjective form meaning 'enough'.
Anh ấy muốn đi chơi nhưng không có tiền đủ.
He wants to go out but doesn't have enough money.
In this sentence, 'đủ' is an adverb meaning 'enough' describing the degree of 'hard work'.
Cô ấy làm việc đủ chăm chỉ để được thăng chức.
She works hard enough to get promoted.
In this instance, 'đủ' is used as an adverb to express the adequacy ('well enough') of students' scores.