Noah Webster's New International Dictionary of the English Language

1. (v. t.) To draw air audibly up the nose; to snuff; -- sometimes done as a gesture of suspicion, offense, or contempt.

2. (v. t.) To draw in with the breath through the nose; as, to sniff the air of the country.

3. (v. t.) To perceive as by sniffing; to snuff, to scent; to smell; as, to sniff danger.

4. (n.) The act of sniffing; perception by sniffing; that which is taken by sniffing; as, a sniff of air.