A verb (suffix) meaning 'to become (a certain state)'; used as -づく/-つく in compounds (e.g., 色づく, 根づく, 気づく) to indicate that something acquires a certain state.
秋になると山々が色付く。
In autumn, the mountains take on color.
彼は小さな違いにもすぐ気付く性格だ。
He has a personality that notices small differences immediately.
その習慣は地域に長く根付いた。
That custom has long taken root in the region.