This is the 7780th most frequent Chinese word.
长长的
"Long" or "very long".
Here, '长长的' is used as an adjective to describe the noun '河流' (river), emphasizing the elongated nature of the subject.
那是一条长长的河流。
That is a long river.
'长长的' acts as a descriptive word for '头发' (hair), indicating length and beauty.
她有一头长长的头发。
She has long hair.
In this instance, '长长的' functions to describe '街道' (street), focusing on its extensive length.