rar·e·fac·tion 
(râr′ə-făkshən)
(râr′ə-făkshən)n.
1. The condition of being rarefied.
2.
a. A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave.
b. The region in which this occurs.
rar′e·factive adj.
- pull through
- pull together
- pull together
- pullulate
- pullulation
- pull up
- pull-up
- pull up stakes
- pull weight
- pull wires
- pull/yank (someone's) chain
- pulmonary
- pulmonary artery
- pulmonary function test
- pulmonary vein
- pulmonate
- pulmonic
- pulmonologist
- pulmonology
- Pulmozyme
- pulp
- pulpiness
- pulpit
- pulpous
- pulpwood