sniff

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To inhale a short, audible breath through the nose, as in smelling something.
• intransitive verb To sniffle.
• intransitive verb To use the sense of smell, as in savoring or investigating.
• intransitive verb To regard something in a contemptuous or dismissive manner.
• intransitive verb Informal To pry; snoop.
• intransitive verb To inhale forcibly through the nose.
• intransitive verb To smell, as in savoring or investigating.
• intransitive verb To perceive or detect by or as if by sniffing.
• intransitive verb To utter in a contemptuous or haughty manner.
• noun An instance or the sound of sniffing.
• noun Something sniffed or perceived by or as if by sniffing; a whiff.

from The Century Dictionary.

• To draw air through the nose in short audible inspirations, as an expression of scorn; snuff: often with at.
• To draw in with the breath through the nose; smell of with an audible inhalation; snuff: as, to sniff the fragrance of a clover-field.
• To perceive as by snuffing; smell; scent: as, to sniff danger.
• To draw the breath through (the nose) in an unpleasantly audible manner.
• noun The act of sniffing; a single short audible inspiration through the nose.
• noun Perception of smell obtained by inhaling audibly; that which is taken by sniffing: as, a sniff of fresh air.
• noun The sound produced by passing the breath through the nose with a quick effort; a short, quick snuffle.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of sniffing; perception by sniffing; that which is taken by sniffing.
• intransitive verb To draw air audibly up the nose; to snuff; -- sometimes done as a gesture of suspicion, offense, or contempt.
• transitive verb To draw in with the breath through the nose.
• transitive verb To perceive as by sniffing; to snuff, to scent; to smell.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An instance of sniffing.
• noun A quantity of something that is inhaled through the nose
• noun A brief perception
• verb transitive, intransitive To make a short, audible inhalation, through the nose, as if to smell something.
• verb To say something while sniffing, for example in case of illness or unhappiness
• verb transitive To perceive vaguely
• verb To be dismissive or contemptuous of something.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb inhale audibly through the nose
• noun sensing an odor by inhaling through the nose
• verb perceive by inhaling through the nose