Yesternoon is a rarely used word that refers to the period of time between yesterday afternoon and last night. The IPA phonetic transcription for this word is /ˈjɛstərnuːn/, with the stress on the first syllable. The first syllable "yes-" is pronounced with a short "e" sound, similar to "yet", while the second syllable "-ter-" is pronounced with a short "u" sound, similar to "thumb". The final syllable "-noon" is pronounced with a long "u" sound, similar to "moon".
The word "yesternoon" is derived from two Old English words: "yester" and "noon". "Yester" is a contraction of the Middle English phrase "ye ester", meaning "of yesterday". "Noon" refers to the midday or period around midday. Therefore, "yesternoon" literally means "the noon or midday of yesterday". Over time, the word has evolved to refer more generally to the afternoon or early evening of the previous day.