Source : Webster's Revised Unabridged Dictionary (1913)

Sputum \Spu"tum\, n.; pl. {Sputa}. [L., from spuere, sputum, to
   spit.]
   That which is expectorated; a salival discharge; spittle;
   saliva.

Source : WordNet®

sputum
     n : expectorated matter; saliva mixed with discharges from the
         respiratory passages; in ancient and medieval physiology
         it was believed to cause sluggishness [syn: {phlegm}]
     [also: {sputa} (pl)]