'ill-chosen' is a compound of 'ill' + 'chosen'. 'ill' originates from Old English (e.g. 'yfel'/'ill(e)') and ultimately from Proto-Germanic '*ubilaz', where the prefix/root meant 'bad'. 'chosen' is the past participle of 'choose', which originates from Old English 'ceosan' (from Proto-Germanic '*keusanan'), where the root meant 'to choose.'

'ill' came into Middle and Modern English from Old English forms such as 'yfel'/'ill'. 'chosen' developed as the past participle form of Old English 'ceosan' through Middle English to the Modern English past participle 'chosen'. The compound 'ill-chosen' formed by combining these elements to describe something selected badly.

Initially the components separately meant 'bad' and 'picked/selected'; over time the compound came to be used idiomatically to mean 'poorly or inappropriately chosen' as a single descriptive term.