Definition of yestermorn in English:

yestermorn

Pronunciation /ˈjɛstəmɔːn/

adverb

poetic, archaic, rare
  • On or during the morning of yesterday; yesterday morning.

noun

poetic, archaic, rare
  • The morning of yesterday.

    Now chiefly in historical fiction.

Origin

Early 18th century; earliest use found in Nicholas Rowe (1674–1718), poet and playwright. From yester- + morn.