[mass noun]diminution in the density of something, especially air or a gas (尤指空气、气体)稀薄化,稀薄状态 ■(Medicine)the lessening of density of tissue, especially of nervous tissue or bone (医)(尤指神经组织、骨质)稀疏(状态),疏松(状态)
语源
early 17th cent.: from medieval Latin rarefactio(n-), from the verb rarefacere 'grow thin, become rare'