1 a : a distance below a surface [count] ▪ These fish typically live at depths of 500 feet or more. ▪ Students will test the temperature of the water at different/varying/various depths. ▪ shallow/great depths ▪ The boat sank to a depth of several hundred feet. ▪ measuring the depth of the water/river/sea ▪ the depth of a hole ▪ The pool has a depth of 12 feet. [noncount] ▪ The pool is 12 feet in depth. [=12 feet deep] b [count] : the distance from the front of something to the back —usually singular ▪ Measure the height, width, and depth of the cabinet. ▪ The bench's depth is 22 inches.
2 [count] : an area that exists far below a surface or far inside something : a deep place or area —usually plural ▪ They disappeared into the depths of the forest. ▪ Scientists have begun using the machine to explore the ocean depths. ▪ the black depths of outer space —often used figuratively ▪ The actress must examine her own emotional depths to perform the role successfully. ▪ Around midnight, a loud noise woke us from the depths of sleep. ▪ I knew in the depths of my heart/soul/being [=I believed very strongly] that we would survive. ▪ The memory lies hidden in the depths of her mind. [=she has not thought about the memory in a long time] ▪ in the depths of winter [=in the middle of winter; in the coldest part of winter]
3 [count] a : a very low or bad state or condition —usually plural ▪ After losing his job, he sank into the depths of misery/despair/depression. ▪ The film portrays a family's difficult climb from the depths of poverty. ▪ I can't believe he lied. He's really sunk to new depths. ▪ The team is reaching/plumbing new depths this season. [=the team is playing worse than it ever has before] b : the worst part of something ▪ I began working at the factory during the depth/depths of the Depression.
4 [noncount] : the quality of being deep: such as a : the quality of being strongly felt ▪ We were surprised by the depth of her anger/pain/shame. ▪ He wanted to express the depth of his love for her. ▪ No one doubted the depth of his faith. [=they all knew that his faith was strong] ▪ the depth of her commitment to the project ▪ The dancers expressed great depth of feeling/emotion. b : the quality of being very bad or serious ▪ I was shocked when I realized the depth of the problem. c : the quality of being complete or thorough ▪ We were impressed by the depth [=extent] of her experience/knowledge. ▪ Your essay lacks depth. [=it does not cover its topic in a complete way] d : the quality of being strong in color, taste, etc. ▪ the depth of a color ▪ The wine has great depth of flavor. e : the quality of being low in sound ▪ the depth of his voice f US sports : the quality of having many good players on a team ▪ The team lacks depth this year.