Green’s Dictionary of Slang

1. (orig. US) to walk or move slowly.

1895		J. London ‘’Frisco Kid’s Story’ in High School Aegis X (15 Feb.) 2–3: I wuz mopin’ down de main drag, I mean de main street.
1900		Marvel 21 Dec. 16: I wos moppin down the strete.
1914		Jackson & Hellyer Vocab. Criminal Sl. 60: mope [...] To walk away; to remove one’s presence to another locality or spot.
1929		E. Booth Stealing Through Life 66: Mope! Screw! G’wan – I’ll bust you in the mouth!
1935		N. Algren ‘A Place to Lie Down’ in Texas Stories (1995) 57: Two hungry bums in Texas, mopin’ down the S.P. ties.
1962		Ragen & Finston World’s Toughest Prison 809: mope – To walk away; to leave. [...] To dawdle.
1989		J. Hibberd Memoirs of an Old Bastard 146: She moped off looking like a bedraggled and stunted red setter.

2. to desert or escape.

1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.
1928		R.J. Tasker Grimhaven 180: Then we moped because the bottles and stoppers had the beef by that time and there was nothing for us to do but hop in the rattle and jar, and powder.
1935		W. Mahoney ‘The Ruse in Cocaine Alley’ in Und. Detective Mar. 🌐 Why the hell didn’t you nab the rat in Mondell’s joint? He’ll mope plenty fast now.
1950		Goldin et al. DAUL 140/2: Mope, v. 1. To depart quickly, especially from an area in which police are active. [...] 3. (P) To escape from custody, especially while on the outside of prison walls, without the use of force.

3. (US Und.) to live as a vagrant; thus on the mope, living as a tramp; moper, a tramp; moping, mopery, tramping.

1930		‘Dean Stiff’ Milk and Honey Route 97: Mopery is still a lower order of bread winning. [...] One form of moping is to hang around the missions and get saved. [Ibid.] 98: The moper is generally a bum of one kind or other.
1949		Monteleone Criminal Sl. (rev. edn).