Merriam-Webster Collegiate Dictionary - ash wednesday

 noun  Date: 14th century the first day of Lent — see Easter table ASH  I. noun  Etymology: Middle English asshe, from Old English ?sc; akin to Old High German ask ~, Latin ornus mountain ~  Date: before 12th century  1. any of a genus (Fraxinus) of trees of the olive family with pinnate leaves, thin furrowed bark, and gray branchlets  2. the tough elastic wood of an ~  3. Old English ?sc, name of the corresponding runic letter the ligature ? used in Old English and some phonetic alphabets to represent a low front vowel a  II. noun  Usage: often attributive  Etymology: Middle English asshe, from Old English asce — more at arid  Date: before 12th century  1. something that symbolizes grief, repentance, or humiliation  2.  a. the solid residue left when combustible material is thoroughly burned or is oxidized by chemical means  b. fine particles of mineral matter from a volcanic vent  3. plural the remains of the dead human body after cremation or disintegration  4. plural deathly pallor the lip of ~es and the cheek of flame — Lord Byron  5. plural ruins  • ~less adjective  III. transitive verb  Date: circa 1894 to convert into ~