The term 'abruptly-declined' is a compound word formed from 'abruptly' and 'declined'. 'Abruptly' originates from Latin 'abruptus', meaning 'broken off', and 'declined' comes from Latin 'declinare', meaning 'to bend down'.

'Abruptly' and 'declined' were used separately in Middle English and later combined to form the modern compound adjective 'abruptly-declined'.

Initially, 'abruptly' meant 'suddenly' and 'declined' meant 'bent down', but together they evolved to describe a sudden decrease.