The spelling of the word "Guillevat" can be explained through the use of IPA phonetic transcription. The first syllable, "guil", is pronounced with a hard "g" as in "goose" followed by a "w" sound. The second syllable, "le", is pronounced with a short "e" sound as in "pet". The final syllable, "vat", is pronounced with a long "a" sound as in "bake" and a soft "t" sound at the end. Therefore, the correct spelling of the word is Guillevat /ˈɡwɪl.ɛ.vat/.