The word "lack-lustre" is spelled with a "k" instead of a "c" due to its origin from Middle English. The pronunciation of the word is represented in IPA phonetic transcription as /ˈlækˌlʌstə/. The first syllable "lack" is pronounced with the short "a" sound as in "cat." The second syllable "lus" is pronounced with the "u" sound as in "up." The final syllable "tre" is pronounced with a schwa sound, which is like a soft "uh" sound.