rarefact

From Middle French raréfaction.

rarefact (third-person singular simple present rarefacts, present participle rarefacting, simple past and past participle rarefacted)

1. (transitive, intransitive) To reduce in density.
   • 2013, Beth Schrope, Surgical and Interventional Ultrasound‎:

     As the ultrasound wave compresses and rarefacts through the medium, it causes microbubbles in the tissue to contract and expand.

• rarefaction