The word is roundest.
Standing
stopping
Teenager
Imprison is a word which has the opposite to liberate and has eight letters
Stopping
Shutting
approach, increase
The opposite of not opening is opening. Eight-letter synonyms for opening, depending on context, include clearing, unlacing, exposing, starting
dismount is the opposite of mount and contains eight letters
Polite is a 6-letter word that is the opposite of rude.
A four letter word and the opposite of fat would be thin.
A five letter word for the opposite of lower is upper.