Green’s Dictionary of Slang

(US black) anyone with a large mouth; also attrib. as nickname; note the jazz musician Louis ‘Satchmo’ (Satchel-Mouth) Armstrong (1900–72); thus cit. 1952.

1934		H. Sebastian ‘Negro Sl. in Lincoln University’ in AS IX:4 288: satchel-mouth A person with an unusually large mouth.
1944		P. Kendall Dict. Service Sl. n.p.: a satchel . . . a gob with a wide mouth.
1946		Four Jumps of Jive [title] Satchel Mouth Baby.
1952		(con. 1948) G. Mandel Flee the Angry Strangers 169: Singin: Poor ole Joe [...] in the best facsimilie of Louis’ sunshine voice she could manage, rattlin’ it ’way down low, as satchelmouth as she could.