The Old English word sæd meant ‘having had one's fill; sated and weary’. Ultimately it is from an Indo-European word, the source also of Latin satis ‘enough’, which itself is the source of satisfy. In the 14th century sad developed the senses ‘steadfast, firm’ and ‘serious, sober’. By the late 15th century it had acquired its modern meaning, ‘sorrowful’. The newest sense, ‘pathetically inadequate or unfashionable’ gained currency in the late 1980s.