Definition of "depression"

It is that Mr. Levi's death could not be dissociated from the major depression with which he was afflicted, and that indeed his suicide proceeded directly from that illness.

1988 December 19, William Styron, “Why Primo Levi Need Not Have Died”, in The New York Times‎

[…] your illness reflects the textbook description of bipolar disorder (euphoric, grandiose, manic highs followed by deep depressions, […]

2011 February 28, David J. Miklowitz, The Bipolar Disorder Survival Guide, Second Edition: What You and Your Family Need to Know, Guilford Press, page 106

His first major breakdown occurred when his son was five years old; he continued to go to pieces periodically, with a particularly deep depression that lasted from the time Bill was in sixth grade until the time he finished junior high […]

2014 September 16, Andrew Solomon, The Noonday Demon: An Atlas Of Depression, Simon and Schuster, page 73

Many alcoholics who die from suicide suffer from deep depressions that are quite frequently protracted, […]

2016 January 14, Danuta Wasserman, Suicide: An unnecessary death, Oxford University Press

It was not far from the house; but the ground sank into a depression there, and the ridge of it behind shut out everything except just the roof of the tallest hayrick. As one sat on the sward behind the elm, with the back turned on the rick and nothing in front but the tall elms and the oaks in the other hedge, it was quite easy to fancy it the verge of the prairie with the backwoods close by.

1879, R[ichard] J[efferies], chapter 1, in The Amateur Poacher, London: Smith, Elder, & Co., […]