Without the singular number.

The earthy particles of combustible substances remaining after combustion; as of wood or coal.

The remains of the human body when burnt. Hence figuratively, a dead body or corpse.

In scripture, ashes is used to denote vileness, meanness, frailty, or humiliation. I who am but dust and ashes. Genesis 18:27. I abhor myself and repent in dust and ashes. Job 42:6.