'old-fashionedness' is a modern English formation, built from the adjective 'old-fashioned' (meaning 'in an old style') plus the noun-forming suffix '-ness'. 'old-fashioned' itself combines 'old' + 'fashioned' (past participle of 'fashion').

'fashion' originates from Old French 'façon' (or Medieval Latin 'factio'), ultimately from Latin 'facere' meaning 'to make'. 'fashioned' (made or formed) combined with 'old' (from Old English 'eald') produced the adjective 'old-fashioned', and later the noun-forming suffix '-ness' produced 'old-fashionedness'.

Initially the elements referred to 'made in an old way' or 'of an earlier fashion'; over time the compound came to mean more generally 'the quality of being out of date' or 'a preference for older styles'.