The opposite of sudden is gradual.
Sudden
In the opposite direction to the course of acceleration.
The opposite of abrupt could be gradual, slow, or incremental.Calm, kind, nice...
The opposite would be sudden or abrupt, so the adjective could be hurried or instant.
The opposite would be sudden or abrupt, so the word could be quick, rapid, or swift.
A sudden change of direction of a wind, generally the exact opposite way.
A power cut is when the power suddenly goes out or gets shut off. The opposite of this would be a power surge, which is a sudden surge of power.
Acute refers to a sudden onset or short duration of a disease or condition, typically characterized by intense symptoms. It is the opposite of chronic, which refers to long-lasting or recurring conditions.
The word 'fit' is a noun as a word for a sudden violent attack of a disease or condition; a sudden outburst; a word for something that is the right size and shape for someone or something. The noun forms for the verb to fit are fitter and the gerund, fitting. The noun forms for the adjective fit is fitness.
An abnormally high white blood cell count is known as leukocytosis. The opposite is leukocytopenia.
abrupt: blunt, brisk, short, snappy, rude, sharp, sudden, hurried, surprising, quick converse: contrary, opposite, reverse