Thank you for your answers! I was asking because, at least in Spanish or German, we always say "the clouds are hiding the sky", even though it is just a "mass" of clouds in which you cannot distinguish one from the other. And I wanted to know if Klingon works this way or there is another explanation. Maybe it's just as Lieven or ghunchu'wI' said: Klingons think of clouds as an "entity" or something like the word "rock". Or the sentence really means only one cloud, as charghwI' says. Perhaps there is someday a clarification.