to make deep or deeper; to increase the depth of; to sink lower; as, to deepen a well or a channel.-to make darker or more intense; to darken; as, the event deepened the prevailing gloom.-to make more poignant or affecting; to increase in degree; as, to deepen grief or sorrow.-to make more grave or low in tone; as, to deepen the tones of an organ.-to become deeper; as, the water deepens at every cast of the lead; the plot deepens.