Definition of "sub-zero"

sub-zero

adjective
not comparable
1. (of a temperature) below 0°C; freezing cold
  Quotations
  Several days of sub-zero temperatures caused icicles up to 1.5 metres long to form in tunnels across Greater Manchester, Lancashire and Cumbria.
  2021 February 24, “Network News: NR takes pride in track teams as effects of Storm Darcy repelled...”, in RAIL, number 925, page 13
2. (of a temperature) below 0°F (−18°C)