History: What is monophony?

What is monophony?

• Monophony is a capability of an instrument meaning... the instrument can create multiple sounds at the same time.
  That is polyphony.
• Monophony is a capability of an instrument meaning... can create either zero or one pitches at a given time.
  Pitches?
• Monophony is a capability of an instrument meaning... can create either zero or one sounds at a given time.
  Excellent!
• Monophony is a capability of an instrument meaning... the instrument can create multiple pitches at the same time.
  Pitches?