Pronunciation: (sub-zēr'ō), [key]
1. indicating or recording lower than zero on some scale, esp. on the Fahrenheit scale: a week of sub-zero temperatures.
2. characterized by or appropriate for sub-zero temperatures: sub-zero climates; sub-zero clothing for the exploration.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.