noun

• (uncountable) The process by which an organism produces others of its kind; breeding, propagation, procreation, reproduction.
• (countable) The act of increasing or rising; augmentation, amplification, enlargement, escalation, aggrandizement.
• (countable) The result of building up; buildup, accretion.
• (uncountable) The spread of biochemical, nuclear and other weapons of mass destruction to countries not originally involved in developing them.