Green’s Dictionary of Slang

1. to go, to leave.

1905		H. Green Actors’ Boarding House (1906) 26: An’ Johnny McDuff’s mushed without puttin’ sumpin’ in my mitt, too.
1906		‘O. Henry’ ‘An Adjustment of Nature’ Four Million (1915) 106: I never got off the train since I mushed out of Seattle.
1940		S.J. Simonsen Among the Sourdoughs 13: They had a number of expressions [...] ‘mush’ take a walk.
1948		National Geographic Mag. Aug. 235/2: We [...] then ‘mushed on’ to Dam No [DA].
1962		(con. late 1920s) E. Lucia Klondike Kate 268: Mush on and smile became Aunt Kate’s byword in her newfound career [...] ‘When you think your heart is breaking / Mush on and smile.’.
2009		T. Black Gutted 7: I got ready to mush, then: a whimper.

2. to walk.

1946		E. Wilson Pikes Peek or Bust 76: [L]oafing in the Palace Hotel lobby watching the lushes mush in from the Press Club.
1974		(con. late 1930s) E.H. Hunt Undercover 15: This meant a half-mile walk to College Hill, breaking trail as I mushed on numb feet over powder snow and frozen crust.

3. to urge forward.

1990

S. Morgan Homeboy 60: Joe watched Pete mush Daisy toward Burger King for a spot of lunch.