Sort of. It depends what context it is being used in. Gradually almost means that it is slow, but sure.
If the sentence is one like "The pumpkin grew gradually." The opposite would be "The pumpkin grew quickly."
The opposite would be sudden or abrupt, so the word could be quick, rapid, or swift.
Gradual
The opposite of sudden is gradual.
The opposite of abrupt could be gradual, slow, or incremental.Calm, kind, nice...
Sudden
The opposite of abrupt could be gradual, slow, or incremental.Calm, kind, nice...
the answer is Suddenly, all at once.
rapid Or possibly "steep."
The opposite would be sudden or abrupt, so the adjective could be hurried or instant.
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."
It is usually slow and gradual, but such things as storms can cause sudden changes.
Fast, quick or speedy.