This is the 613th most frequent Spanish word.
graves
"Graves" in Spanish refers to something serious, solemn, or severe, or to words with stress on the second-to-last syllable.
In this sentence, 'graves' is used as an adjective meaning serious or severe, describing the noun 'enfermedades' (illnesses).
Las enfermedades graves requieren atención médica inmediata.
Serious illnesses require immediate medical attention.
Here, 'graves' again functions as an adjective meaning severe, describing the noun 'daños' (damages).
En el accidente hubo graves daños materiales.
In the accident, there were serious material damages.
In this example, 'graves' is used as an adjective to describe 'tonos' (tones), meaning low or bass in pitch.