1. That which envelops, wraps up, encases, or surrounds; a wrapper; an inclosing cover; esp., the cover or wrapper of a document, as of a letter. 2. (Astron.) The nebulous covering of the head or nucleus of a comet; -- called also coma. 3. (Fort.) A work of earth, in the form of a single parapet or of a small rampart. It is sometimes raised in...