'well-defined' originates from the combination of 'well,' meaning 'in a good or satisfactory way,' and 'defined,' from Latin 'definire,' meaning 'to limit or determine.'

'defined' changed from the Latin word 'definire' and eventually became the modern English word 'define.'

Initially, 'defined' meant 'to limit or determine,' and over time it evolved into its current meaning of 'clearly outlined or specified.'