lessen['lesən]vt.1.■减少，使变小，使缩小，使减轻：to lessen production costs降低生产成本to lessen the tension减少压力2.■[古语]轻视，藐视；贬低；抹杀：to lessen a person's feat抹杀某人的功绩vi.1.■减少；变小；缩小；减轻：The difference between the city and the countryside lessens gradualy.城乡差别逐渐缩小。conj.1.■[美国方言] 除非(=unless)