Any dog trained by law enforcement to detect drugs, especially marijuana, by smell. I broke out in a cold sweat when I saw them bring the pot sniffers onto the bus. There's no way I'm smuggling dope through the airport—that place is crawling with pot sniffers!

slang One's nose. Put your sniffer up to these roses I just brought in from the garden. Don't they smell divine? The ball hit her right in the sniffer.