thresh: To separate by any mechanical means, e.g. rubbing, shaking, trampling, stamping, beating, or intermittent pressure, the grains of any cereal from the husks and straw; esp. by beating with a flail; now (from the latter part of the eighteenth century) also by the action of revolving mechanism in a mill or machine. Also, to shake out or separate in the same way the seed of any plant.——Oxford English Dictionary

thresh: To remove unwanted plants from a garden or other place to separate grains of corn, wheat etc from the rest of the plant by beating it with a special tool or machine.——Longman Dictionary of Contemporary English  @en