The word "most prejudicious" is often misspelled as "most prejudicial". However, the correct spelling is "prejudicious", with the emphasis on the second syllable. The pronunciation is /prɪˈdʒuːdɪʃəs/, with the "j" sound in "judge" and the "sh" sound in "shoe". The word means harmful or detrimental, and it is most commonly used in legal language. Even though it is not as commonly used as "prejudicial", it is important to spell it correctly to convey the intended meaning.
The word "prejudicious" does not have an established etymology, as it is not a standard English word. It appears to be a derivative of the word "prejudice", meaning to pre-judge or form an opinion about something without full knowledge or understanding. However, the word "prejudicious" itself is not commonly used and may be a rare or archaic term. It is possible that it was coined specifically for a particular context or text but has not entered into standard usage. Without additional context or information, it is difficult to provide a more precise etymology for this word.