[ 'rɛ:rɪfʌɪ ]
(also rarify )
■ verb ( rarefies , ~ing , rarefied ) make or become less dense or solid.
Derivatives
rarefication noun
rarefactive adjective
Origin
ME: from OFr. rarefier , or med. L. rareficare , based on L. rarus 'rare' + facere 'make'.