This is the 10102nd most frequent Polish word.
bieleją
"Bieleją" means "they whiten" or "become white."
Here, 'bieleją' is used as a verb in the present tense, meaning 'to whiten' or 'to become white.' It describes the visual appearance of sails at a distance.
Na horyzoncie bieleją żagle.
On the horizon, the sails whiten.
In this sentence, 'bieleją' describes the gradual change in color of the clouds, typically observed during early morning when the light changes.
Obłoki bieleją na niebie, gdy nadchodzi świt.
The clouds whiten in the sky as dawn approaches.
Here, 'bielejące' is used as an adjective derived from the verb 'bieleją,' implying an ongoing state of becoming white as a result of snow.