Renowned and powerful are synonyms for famous. They contain 8 letters.
renowned, esteemed
An 8 letter word that means the inside of anything might be "interior." This word has 8 letters and would probably fit your crossword puzzle clue.
"Endorsement" is an 8-letter word that means official approval or support.
accurate
transfer
famished
Egoistic
Isolated
birthday
allocate
friction
memorize