This is the 10699th most frequent Portuguese word.
grisalhos
Gray or graying (usually referring to hair).
In this sentence, 'grisalhos' is used as an adjective describing the color of the grandfather's hair, indicating it is gray.
Os cabelos grisalhos do avô são muito elegantes.
The grandfather's gray hair is very elegant.
Here, 'grisalhos' functions as an adjective to describe strands of hair, showing that the term applies to singular elements of a collection.
Ele já começou a notar alguns fios grisalhos entre os seus cabelos.
He has already started noticing some gray strands among his hair.
In this example, 'grisalhas' as a feminine plural adjective achieves a figurative usage when describing the color of leaves, deriving a poetic imagery from the term.