The word "un aptest" is spelled with the prefix "un-" which means "not" followed by "aptest" which is the superlative form of "apt". The pronunciation of "aptest" is /ˈæptɪst/ with the stress on the first syllable. When adding the prefix "un-", the pronunciation changes to /ʌn ˈæptɪst/. The word itself means "not most suitable" or "least suitable". It is commonly used in formal writing and can be replaced with simpler words like "inappropriate" or "unsuitable".