thumb index thumb holing • thumbkin · · · Info · Definitions · Characters · · thumb index · · Text Common · · Latin · · Scripts 11 · · Length 3 · · Syllables Definitions · · · (noun) one of a series of rounded notches in the fore edge of a book to indicate sections. Synonyms: thumb index. · · Noun Definition 1 Characters · · space U+0020 b latin small letter b U+0062 d latin small letter d U+0064 e latin small letter e U+0065 h latin small letter h U+0068 i latin small letter i U+0069 m latin small letter m U+006D n latin small letter n U+006E t latin small letter t U+0074 u latin small letter u U+0075 x latin small letter x U+0078