The correct spelling of the phrase "most critic" is actually "most critical." The final letter "al" is important to show that the word is an adjective, indicating great importance or necessity. The IPA phonetic transcription for "most critical" is /moʊst ˈkrɪt ɪ kəl/, with the stress on the second syllable of "critical." It's important to double-check your spelling, especially when using critical language in your writing.
The term most critic does not have any particular etymology as it does not form a recognized word or phrase. Most is a superlative adjective and critic is a noun meaning someone who evaluates and analyzes something critically. However, if you are referring to the phrase critics, then the word critic has its roots in the Latin word criticus, which means able to make judgments. It is derived from the Greek word krites, meaning judge, which ultimately comes from the verb krinein meaning to separate or to decide.