The word "athericerous" may seem daunting at first sight, but its spelling can be broken down using IPA phonetic transcription. Firstly, we have the "a" sound as in "cat" followed by "th" as in "thin". Next, there's the "er" sound as in "her" and "i" as in "bit". Lastly, "ce" is pronounced like "sh" and "ous" sounds like "us". Putting it all together, we get "a-TH-er-i-ce-rous". Despite its complexity, the word is rarely used in everyday conversation.
Pert. to.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.