1rare Any of various fishes with a relatively large mouth; (in early use) specifically the American angler, Lophius americanus.
2slang (A nickname for) a person having a large mouth.
Best known as a nickname of Louis Armstrong (1900–71), American jazz trumpeter and singer (usually shortened to Satchmo or Satch).
Early 20th century; earliest use found in Henry Fowler (1858–1933), lexicographer and grammarian. From satchel + mouth, the mouth being compared to an open satchel.