Shneidman used the term in relation to suicide in the same paragraph as the definition: "Suicide is caused by psychache." (italics in the original)
Clinicians and scientists can "miss the mark" if they ignore this internal distress when trying to explain suicide by such variables as age, sex, and socioeconomic level.
Schneidman, E. S. (1993). Commentary: Suicide as psychache. The Journal of Mental Disease, 181, (3), 145-147.