breather

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

• noun One that breathes, especially in a specified manner.
• noun Informal A short rest period.
• noun Informal An activity, such as strenuous exercise, that causes difficult breathing.
• noun A small vent allowing the passage of gas or liquid to or from an enclosed area.

from The Century Dictionary.

• noun One who breathes or lives.
• noun One who utters or whispers.
• noun One who animates or inspires.
• noun Anything, as a walk, gymnastic exercise, etc., that stimulates or gives healthy action to the breathing organs.

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

• noun One who breathes.
• noun One who lives.
• noun One who utters.
• noun One who animates or inspires.
• noun colloq. That which puts one out of breath, as violent exercise.
• noun colloq. a pause to catch one's breath, or for some other form of rest or refreshment; -- often used in the phrase to take a breather, i.e. to pause for refreshment.
• noun a vent in a container to allow equalization of internal and external pressure.
• noun an air intake pipe to provide air to machinery or people submerged or otherwise sealed off from the outside.

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

• noun Something or someone that breathes.
• noun A short break; a rest or respite.
• noun physics A spatially localized, time-periodic excitation in a one-dimensional lattice.
• noun colloquial, dated That which puts one out of breath, such as violent exercise.

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

• noun air passage provided by a retractable device containing intake and exhaust pipes; permits a submarine to stay submerged for extended periods of time
• noun a short respite