/ Dictionary / Index P pneumothorax: Meaning and Definition of Find definitions for: pneu•mo•tho•rax Pronunciation: (n"mu-thôr'aks, -thōr'-, ny"-), [key] — n. Pathol. the presence of air or gas in the pleural cavity. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: pneumothorax (Thesaurus) pneumonoultramicroscopicsilicovolcanoconiosis pneumotropic Related Content Daily Word Quiz: sylvan Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language