• in‧stru‧ment [countable]
• 1

  tool

  a small tool used in work such as science or medicine:
• surgical instruments
• 2

  music

  an object used for producing music, such as a piano or violin[= musical instrument; ↪ instrumental, instrumentalist]:
• electronic instruments
• brass/wind/percussion/stringed etc instrument
• 3

  for measuring

  a piece of equipment for measuring and showing distance, speed, temperature etc:
• a failure of the flight instruments
• sensitive earthquake-detecting instruments
• 4

  method

   [usually singular] something or someone that is used to get a particular result
• instrument of
• Interest rates are an important instrument of economic policy.
• instrument for (doing) something
• Good management should be an instrument for innovation.
• 5

  for hurting

  something that is used to hit or hurt someone:
• Death was due to a blow on the head with a blunt instrument.
• instrument of torture (=an object used to make people suffer pain until they give information)
• 6

   instrument of fate/God

  literary someone or something that is used by a power beyond our control

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary