Green’s Dictionary of Slang

mooch v.

also mouch
[for a detailed analysis see Liberman (2008 157ff) who sees it as one of a number of terms found in pan-European slangs meaning concealment and/or cheating; these in turn suggest an old Germanic word with cognates in Celtic and Latin with a basic meaning of darkness or mist. The proposed ety of OF muser, to hide, is seen as a descendant of these, rather than the origin ]

1. [early 19C+] (also mootch) to pilfer, to steal; thus mooching/mouching n. and adj.

2. [mid-19C+] (also moose) often constr. with along, off, out etc, to walk, to go, to amble along.

3. [mid-19C+] to beg, to sponge, to cadge, also vtr, to beg from; thus mooching n.

4. [late 19C+] (also smooch) to loaf around.

5. [late 19C+] (UK tramp) to live as a tramp.

6. [1910s+] to take.

7. [1910s+] (US) to enter surreptitiously.

8. [20C+] (Ulster) to play truant; esp. as on the mooch

In phrases

mooch off (v.) (also mouch off)

[1920s+] (US) to laze around.

mooch the stem (v.) [main stem n. (4)]

[20C+] (US) to beg in a city’s main street.

on the mooch

1. [mid-19C+] living as a professional beggar.

2. [mid-19C+] in search of a given commodity, e.g. money or drugs.

3. [late 19C] (also on the mouch) wandering about.

4. [late 19C] on the lookout.

5. [20C+] (Irish) playing truant.

6. [1940s–50s] (drugs) addicted to drugs.