To make less; to reduce; to make smaller, or fewer; to diminish; to lower; to degrade; as, to lessen a kingdom, or a population; to lessen speed, rank, fortune
To become less; to shrink; to contract; to decrease; to be diminished; as, the apparent magnitude of objects lessens as we recede from them; his care, or his wealth, lessened
decrease in size, extent, or range; "The amount of homework decreased towards the end of the semester"; "The cabin pressure fell dramatically"; "her weight fall to under a hundred pounds"; "his voice fell to a whisper"
If something lessens or you lessen it, it becomes smaller in size, amount, degree, or importance. He is used to a lot of attention from his wife, which will inevitably lessen when the baby is born Make sure that your immunisations are up to date to lessen the risk of serious illness. increase + lessening less·en·ing increased trade and a lessening of tension on the border. to become smaller in size, importance, or value, or make something do this = reduce lessen the risk/chance/possibility etc (of sth)