Subzero

Adjective

 * 1) Less than zero, most commonly used to refer to temperature.

Thesaurus
Siberian, algid, arctic, below zero, biting, bitter, bitterly cold, bleak, boreal, brisk, brumal, cold, cold as charity, cold as death, cold as ice, cold as marble, crisp, cutting, freezing, freezing cold, frigid, gelid, glacial, hibernal, hiemal, hyperborean, ice-cold, ice-encrusted, icelike, icy, inclement, keen, nipping, nippy, numbing, penetrating, piercing, pinching, raw, rigorous, severe, sharp, sleety, slushy, snappy, stone-cold, supercooled, winterbound, winterlike, wintery, wintry

Alternative forms

 * sub-zero