Deepen

verb

1. To make deep or deeper

   "They deepened the well by 200 feet."

2. To make darker or more intense; to darken

   "The event deepened the prevailing gloom."

3. To make more poignant or affecting; to increase in degree

   "News of her death deepened my sorrow."

4. To make lower in tone

   "The tuner deepened the tone of the organ."

5. To make more thorough or extensive.

   "The class deepened my understanding of the subject."