Rarefy

Rar″e‐fy (răr″ē̍‐fī; 277), v. t. [imp. & p. p.Rarefied (–fīd); p. pr. & vb. n.Rarefying (–fī′ĭng).] [F. raréfier; L. rarus rare + -ficare (in comp.) to make; cf. L. rarefacere. See -fy.] To make rare, thin, porous, or less dense; to expand or enlarge without adding any new portion of matter to; — opposed to condense.