To inhale audibly through the nose, often to detect a smell. The dog sniffed the ground, searching for the scent of the rabbit.
To express disapproval or contempt by inhaling audibly through the nose. She sniffed at the suggestion, clearly unimpressed by the idea.
To perceive or detect by or as if by smelling. He sniffed the air, trying to determine if dinner was ready.
To take in a small amount of a substance through the nose. He sniffed the powder cautiously, unsure of its effects.