Mondayday of the week between Sunday and Tuesday. It gets its name from the Mona, the Saxon Moon god.
Monday is sometimes held to be the first day of the week (especially in modern Europe, see ISO 8601), and sometimes the second day (a traditional view derived from ancient Jews and still standard in the United States). For this reason, the name for the day in Arabic, Greek, and Portuguese is "second day".
Modern culture usually looks at Monday as the beginning of the work week, as it is typically Monday when adults go back to work and children back to school after the weekend, hence the colloquial "illness" Mondayitis. A possible reason for Mondayitis is that human circadian rhythms are incompatible with the normal 40-hour working week.
In the popular rhyme, "Monday's Child is fair of face".