No they're antonyms
The Esperanto words for sudden and gradual are subita and laŭgrada.
The opposite of sudden is gradual.
The antonym form of the word 'gradual' is sudden.
Gradual
almost
unexpected or sudden
A palindrome that is a synonym of "sudden noise" is "pop," as it reads the same forwards and backwards.
Sudden
sudden Widespread Gradual Time
Slowly, poco a poco, little by little.
Immediate Sudden
Unexpected