\At*ten`u*a"tion\, n. [L. attenuatio: cf. F.
att['e]nuation.]
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.