Attenuation

At·ten·u·a·tion

Attenuation

n.
  1. The act or process of making slender, or the state of being slender; emaciation.
  2. The act of attenuating; the act of making thin or less dense, or of rarefying, as fluids or gases.
  3. The process of weakening in intensity; diminution of virulence; as, the attenuation of virus.