If the sky is overcast, a thick layer of cloud covers it, so the day looks grey and a bit dark. You still have daylight, but you cannot see the sun.

If the sky is overcast如果天空overcast a thick layer of cloud covers it就是有一層厚厚的雲蓋住了天空 so the day looks grey and a bit dark讓這一天看起來灰灰的、有點暗 You你 still have daylight還是有白天的光 but you cannot see the sun只是看不到太陽

Weather reports say overcast for a fully cloudy sky — cloudier than “partly cloudy.” You can say an overcast sky, an overcast day, or it is overcast. It is a calm, ordinary word; not slang, not fancy.

Weather reports say overcast for a fully cloudy sky氣象報告裡，全部被雲蓋住的天空叫overcast cloudier than “partly cloudy.”比「partly cloudy」還要陰 You can say an overcast sky, an overcast day, or it is overcast你可以說an overcast sky、an overcast day，或者it is overcast It它 is a calm, ordinary word是個平實、普通的字 not slang, not fancy不是俚語，也不花俏

People also use it as a noun for that grey cover: the morning overcast. Though actually, the old piece “cast” is the verb to throw: the picture is clouds thrown over the sky.

People also use it as a noun大家也會把它當名詞用 for that grey cover指那層灰灰的雲蓋 the morning overcastthe morning overcast（早晨的雲層） Though actually不過其實 the old piece “cast” is the verb to throw裡面舊的那個字根「cast」是動詞「丟、拋」 the picture is clouds thrown over the sky畫面是雲被拋撒到天空上

(There is also an overcast stitch in sewing, but that is a different job for the same spelling.)

(There is also an overcast stitch in sewing（縫紉裡也有一種overcast stitch（鎖邊縫） but that is a different job for the same spelling.)但那是同樣拼法做不同的工作）