An antidisestablishmentarianist is another name for an antidisestablishmentarian, a person who believes that the Church of England should retain its formal constitutional relationship with the state.
Antidisestablishmentarianist is a word with 11 syllables.
Antidisestablishmentarianist. (An-ti-dis-es-tab-lish-ment-ar-i-an-ist) That's the only 11 syllable word I can think of.