This is the 14181st most frequent German word.
graue
"Graue" means "gray" in English.
The word 'graue' is used here attributively as an adjective modifying the noun 'Himmel' (sky), describing its color.
Der graue Himmel kündigt Regen an.
The gray sky is announcing rain.
In this sentence, 'graue' functions as a descriptive adjective, agreeing in gender, number, and case with the noun 'Jacke' (jacket).
Ich trage eine graue Jacke.
I am wearing a gray jacket.
Here, 'grauen' is the inflected form of the adjective 'grau' used in the plural to describe the noun 'Katzen' (cats).