Choice of Words: Gray describes the color of the clouds, moved is the past tense of the verb 'move', which means to change position, and slowly describes the pace at which the clouds were moving.
Alternative Expressions
The dark clouds drifted lazily.
Meaning: This sentence describes the movement of clouds in the sky. The clouds are dark in color and they are moving slowly and effortlessly.
Choice of Words: The word "dark" describes the color of the clouds, which is a deep or intense shade of black or gray. "Clouds" are the fluffy white or gray things that float in the sky. "Drifted" means that the clouds were moving slowly and effortlessly, like a feather floating on the wind. "Lazily" means that the clouds were moving in a relaxed and unhurried manner.
The ominous clouds crept across the sky.
Meaning: This sentence describes the movement of clouds in the sky. The clouds are dark and threatening and they are moving slowly and stealthily across the sky.
Choice of Words: The word "ominous" describes something that is threatening or foreboding. "Clouds" are the fluffy white or gray things that float in the sky. "Crept" means that the clouds were moving slowly and stealthily, like a cat stalking its prey. "Across" means that the clouds were moving from one side of the sky to the other.