Monday was a day of the week.
Bank holidays were usually held on Mondays. (TV: The Idiot's Lantern, The Rings of Akhaten)
Sergeant Paterson taught physical fitness to older men on Mondays. (TV: Survival)
The Smudgelings got together on Mondays. (PROSE: Mad Dogs and Englishmen)
Gita Chandra once jokingly asked Sarah Jane Smith whether she saved the world every day, "or is it just on Mondays?" (TV: The Day of the Clown)
Clara Oswald faced a Skovox Blitzer "on a miserable wet Monday morning." (TV: The Caretaker, COMIC: Terrorformer)
The Judoon put Gloucester into lockdown on a Monday in 2020, in order to hunt down the Doctor, who was in hiding under a Chameleon Arch as "Ruth Clayton". (TV: Fugitive of the Judoon)