What is the X in X-mas?
"field of granular snow, firn," 1843, from French névé (19c.), probably from Savoyard névi "mass of snow," from Latin nivem (nominative nix) "snow" (cf. French neige), from PIE root *sneigwh- "snow, to snow" (see snow (n.)).
The upper part of a glacier, consisting of hardened snow.
The granular snow typically found in such a field.