unretirement noun [U, C]
UK /ʌn.rɪˈtaɪə.mənt/ US /ʌn.rɪˈtaɪr.mənt/
the act of going back to work after you have retired

Amid a hot labor market and high inflation, retired workers are returning to work at a rising rate. ‘Unretirements’ are on the rise as workers who previously said they were retired are now taking jobs again. As of March 2022, 3.2% of workers who were retired a year earlier are now employed.
[hiringlab.org, 14 April 2022]

youth transplant noun [C]
UK /ˈjuːθ ˌtræns.plɑːnt / US /ˈjuːθ ˌtræns.plænt/
a way of making people age more slowly by injecting them with chemicals that are the same as those found in the bodies of young people

Science is beginning to discover that “youth transplants” really can slow down the ageing process. The fountain of youth, it seems, is youth itself. Although nobody is suggesting we siphon the bodily fluids of youngsters into our elderly, it opens the door to artificially replicating the cocktail of chemicals found in young people. Young people have more powerful cells which operate more efficiently and could restore vitality to ageing systems.
[telegraph.co.uk, 14 May 2022]

baby bust noun [C]
/ˈbeɪ.bi ˌbʌst/
a large decrease in the number of babies born among a particular group of people during a particular time

A drop in births for just a year would not be a major problem on its own, but this likely baby bust will come after many years of falling birthrates. U.S. annual births fell to 3.75 million in 2019 from 4.3 million in 2007. Together with the Covid baby bust, these trends suggest that our country could see a multiyear reduction in births that approaches — in reverse — the swell in births that led to the baby boom generation born after World War II.
[nytimes.com, 4 March 2021]

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