Understand 'onset' signifies the precise moment something starts, often used for events or processes. He noticed the onset of symptoms just after lunch.
Pro Tip 2/3
Abstract Concepts
'Onset' can mark the beginning of non-physical things, like emotions or eras. The onset of her anxiety came without warning.
Pro Tip 3/3
Not Instantaneous
The 'onset' implies a development that follows, not an instant change. At the onset of darkness, the streets became deserted.