This is the 7989th most frequent Spanish word.
morena
"Morena" means a brunette or dark-skinned/dark-haired woman.
Here, 'morena' describes the dark color of the sand, adapting to its context as an adjective.
Prefiero la playa donde la arena es morena.
I prefer the beach where the sand is dark.
In this instance, 'morena' is the noun referring to a type of marine creature, the moray eel.
El pez morena se esconde entre las rocas.
The moray eel hides among the rocks.
In this sentence, 'morena' refers to a woman with dark hair color, often brunette in English.