Spellman’s Syllabary is a guide to symbols used to represent syllables.
One of the many books Hermione consulted as she worked on her Ancient Runes homework in the common room (OP26, HBP24). She took it along on the quest to find Horcruxes in case she would need to translate runes (DH6). It came in handy (DH16).
"Spellman" is humorous because "spell" can refer to magic or to spelling out a word.
A syllabary is a set of symbols where each one represents a specific syllable. The title of this books suggests that the words used to cast spells are sometimes represented by sets of symbols other than our usual alphabet. However, since English and Latin are not well suited at all for a syllabary, this book might actually be designed for use with another language or perhaps a separate spellcasting language which is built with sound chunks which have discrete magical meanings. - SVA