Source : Webster's Revised Unabridged Dictionary (1913)

Spirillum \Spi*ril"lum\, n. [NL., dim. of L. spira a coil.]
   (Biol.)
   A genus of common motile micro["o]rganisms ({Spirobacteria})
   having the form of spiral-shaped filaments. One species is
   said to be the cause of relapsing fever.

Source : WordNet®

spirillum
     n 1: spirally twisted elongate rodlike bacteria usually living in
          stagnant water
     2: any flagellated aerobic bacteria having a spirally twisted
        rodlike form [syn: {spirilla}]
     [also: {spirilla} (pl)]