Definitions of instrument:

• noun:   the means whereby some act is accomplished

  Example: "My greed was the instrument of my destruction"

• noun:   a device that requires skill for proper use
• noun:   a person used by another to gain an end
• noun:   any of various devices or contrivances that can be used to produce musical tones or sounds
• noun:   the semantic role of the entity (usually inanimate) that the agent uses to perform an action or start a process
• noun:   (law) a document that states some contractual relationship or grants some right
• verb:   equip with instruments for measuring, recording, or controlling
• verb:   address a legal document to
• verb:   write an instrumental score for