Sharp
brilliant.
A five letter word that is the opposite of the word "gradual" and contains a second letter of "l" is a popular word game answer. The five letter word being sought is "fleet."
Dull?
A five letter word for the opposite of lower is upper.
the opposite of dull is bright or interesting...
A five letter word meaning the opposite of hurry would be dally. There may well be others
Dull
least
front
night
giant
plain