Dash is a topographic name for someone who lived near an ash tree, or a habitational name from a place named with the Old English word æsc (Ash).
Family name origins & meanings
English : topographic name for someone who lived near an ash
tree, or a habitational name from a place named with the Old English
word æsc (see Ash). The Anglo-Norman French
preposition de ‘of’, ‘from’ has become fused to the name.