rar·e·fy also rar·i·fy (râr'ə-fī') v.
rar·e·fied also rar·i·fied, rar·e·fy·ing also rar·i·fy·ing, rar·e·fies also rar·i·fies
v.
tr.
To make thin, less compact, or less dense.
To purify or refine.
v.
intr. To become thin or less compact or dense.
[Middle English rarefien, from Old French rarefier, from Medieval Latin rārificāre, alteration of Latin rārēfacere : rārus, rare + facere, to make; see dhē- in Indo-European roots.] rar'e·fi'a·ble adj.