sesquipedalianism - Definitions from Dictionary.com

ses·qui·pe·da·li·an /ˌsɛskwɪpɪˈdeɪliən, -ˈdeɪlyən/ Pronunciation Key - Show Spelled Pronunciation[ses-kwi-pi-dey-lee-uhn, -deyl-yuhn] Pronunciation Key - Show IPA Pronunciation
–adjective Also, ses·quip·e·dal /sɛsˈkwɪpɪdl/ Pronunciation Key - Show Spelled Pronunciation[ses-kwip-i-dl] Pronunciation Key - Show IPA Pronunciation.
1. given to using long words.
2. (of a word) containing many syllables.