This is the 13620th most frequent German word.
dunkler
"Dunkler" means "darker" in English.
Here, 'dunkler' is used as a comparative form of 'dunkel' (dark), modified by 'werdenden' (becoming), describing an attribute of the clouds.
Die dunkler werdenden Wolken kündigen Regen an.
The darkening clouds indicate rain.
In this sentence, 'dunkler' is the comparative form, describing the relative darkness of the room compared to the outside.
Im Raum war es dunkler als draußen.
The room was darker than outside.
Here, 'dunkler' modifies 'Kleidung' (clothing) as an adjective in its comparative form, enhancing the description of the clothing's color.