If something smoldered, it burned and made smoke without flames.
Smoldered can make people think of danger, fire, or something not completely gone.
Examples:
The campfire smoldered all night.
The wood smoldered after the fire went out.
The fire smoldered quietly in the fireplace.
The old fire smoldered and smoked.
The volcano smoldered for days before erupting.
The embers smoldered in the dark.