Definition of "worst-case"

worst-case

adjective
not comparable
1. In the least favorable of all possible circumstances.
  Quotations
  In the summer, the RSSB calculated that passengers stood a 1-in-11,000 chance of catching COVID-19 on a train - a statistic it felt was actually a worst-case figure, with the risk probably even lower.
  2020 November 18, Paul Clifton, “We have always cleaned trains. Now, we are sanitising them”, in Rail, pages 32–33