'gladness' originates from Old English, specifically the word 'glæd', where 'glæd' meant 'bright, shining; joyful'.

'glæd' changed into Middle English 'glad', and with the native suffix '-ness' (Old English '-nes(s)') formed the Modern English word 'gladness'.

Initially it meant 'bright' or 'shining' and later shifted to the emotional sense 'pleased' or 'joyful', which led to the noun meaning 'the state of being glad'.