Source : Webster's Revised Unabridged Dictionary (1913)

Bloodletting \Blood"let`ting\, n. (Med.)
   The act or process of letting blood or bleeding, as by
   opening a vein or artery, or by cupping or leeches; -- esp.
   applied to venesection.

Source : WordNet®

bloodletting
     n 1: formerly used as a treatment to reduce excess blood (one of
          the four humors of medieval medicine)
     2: indiscriminate slaughter [syn: {bloodbath}, {bloodshed}, {battue}]