Debauch is an old word that speaks to an older time. It means to destroy the morals of someone. If you debauch a young girl, you introduce her to immoral activities. A debauch is also an excessive amount of eating or drinking.
To understand debauch, you have to understand a context in which women were considered pure because they were virgins and also because they were generally innocent. Men—often the kind whose lives were spent in a debauch of eating, drinking, using bad language, smoking, etc.—would debauch these women, ruining them for all time, in a bout of debauchery.