'unsuitably-dressed' originates from the prefix 'un-' meaning 'not,' combined with 'suitably,' which comes from 'suitable,' and 'dressed,' meaning 'clothed.'

'unsuitably' evolved from 'suitable' with the prefix 'un-' added to negate the meaning, and 'dressed' has remained consistent in its meaning of being clothed.

Initially, it meant 'not dressed in a suitable manner,' and this meaning has largely remained the same in modern usage.