(1):
(v. t.) To make darker or more intense; to darken; as, the event deepened the prevailing gloom.
(2):
(v. t.) To make more poignant or affecting; to increase in degree; as, to deepen grief or sorrow.
(3):
(v. t.) To make more grave or low in tone; as, to deepen the tones of an organ.
(4):
(v. t.) To make deep or deeper; to increase the depth of; to sink lower; as, to deepen a well or a channel.
(5):
(v. i.) To become deeper; as, the water deepens at every cast of the lead; the plot deepens.