Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
red-letter is an adjective meaning "memorable for being a special occasion". It carries one recorded sense.
memorable for being a special occasion
“on red-letter nights a large gathering greeted the celebrity”
Definitions, synonyms and semantic relations for red-letter come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.