The word idempotent, as used in this context in the specifications, is (pseudo)mathematical jargon…and should not be taken too seriously or literally here. The phrase “no lasting observable effect on the state of the world” isn’t of course very exact either, and isn’t really the same thing. Idempotent processing, as defined above, does not exclude fundamental changes, only that processing the same data twice has the same effect as processing it once.

re: diff b/w Methods GET and POST in HTML forms

Language Log: Intonation contours and polonium poisoning

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.