Definitions of thrash:

• noun:   a swimming kick used while treading water
• verb:   give a thrashing to; beat hard
• verb:   beat the seeds out of a grain
• verb:   move data into and out of core rather than performing useful computation

  Example: "The system is thrashing again!"

• verb:   beat so fast that (the heart's) output starts dropping until (it) does not manage to pump out blood at all
• verb:   beat thoroughly in a competition or fight
• verb:   move or stir about violently

  Example: "The feverish patient thrashed around in his bed"

• verb:   dance the slam dance
• name:  A surname (rare: 1 in 33333 families; popularity rank in the U.S.: #4277)