'well-chosen' is a compound of 'well' and 'chosen', where 'well' means 'in a good or satisfactory way' and 'chosen' is the past participle of 'choose', meaning 'selected'.

'Well-chosen' formed in English by combining 'well' and 'chosen', following the pattern of similar compound adjectives.

Initially, it simply meant 'chosen in a good way', and over time it has come to mean 'selected with care and appropriateness'.