is best a closed syllable word

The word "best" is a closed syllable word. A closed syllable contains one vowel that is followed (or closed in) by one or more consonants, and the vowel sound is short. In the case of "best," the vowel "e" is followed by the consonants "s" and "t," which closes the syllable and produces a short vowel sound. Hence "best" fits the definition of a closed syllable word perfectly.