Wikia

Rime
Rime (Passive) Passive Your Obliterate has a 45% chance to cause your next Howling Blast or Icy Touch to consume no runes.
Usable by
Class	Death knight
Properties
School	Physical
Talents
Specialization	Frost
Level required	70
Related buff
Magic Freezing Fog Your next Icy Touch or Howling Blast will consume no runes and generate no Runic Power. Duration: 15 seconds

Rime is a passive death knight ability learned at level 70 for death knights with the frost specialization.

Patch changes

/ Patch 4.0.1 (12-Oct-2010): Moved from tier 6 to tier 4. No longer increases critical strike chance of Icy Touch or Obliterate. Proc chance increased to 15/30/45% and affects Icy Touch, but no longer resets the cooldown.
Patch 3.3.3 (2010-03-23): Dual wielding will no longer grant two chances to proc this effect from Obliterate.
Patch 3.1.0 (14-Apr-2009): When this talent triggers, it also resets the cooldown on Howling Blast. This talent is now triggered by Obliterate instead of Icy Touch.