Source : Webster's Revised Unabridged Dictionary (1913)

Quarterstaff \Quar"ter*staff`\, n.; pl. {Quarterstaves}.
   A long and stout staff formerly used as a weapon of defense
   and offense; -- so called because in holding it one hand was
   placed in the middle, and the other between the middle and
   the end.

Source : WordNet®

quarterstaff
     n : a long stout staff used as a weapon
     [also: {quarterstaves} (pl)]