2. Adjective. (informal) feeling ill, especially used re clergymen after working all day Sunday ¹
3. Adjective. (informal) hungover after a weekend of drinking (as a presumed contributing explanation for a clergyman feeling Mondayish) ¹
4. Adjective. (informal) grumpy and disheartened on returning to work on a Monday after the weekend ¹
¹ Source: wiktionary.com