mindmap root((即兴)) extemporaneous stresses the demands imposed by the occasion or situation and may imply a certain sketchiness or roughness: an ~ shelter prompted by the sudden storm. improvised implies the constructing or devising of something without advance knowledge, thought, or preparation and often without the necessary or proper equipment: ~ a barbeque pit at the campground. impromptu stresses the immediacy and the spontaneity of the thing composed or devised: an ~ speech at an awards ceremony. offhand strongly implies casualness, carelessness, or indifference: his ~ remarks often got him into trouble. unpremeditated suggests some strong, often suddenly provoked emotion that impels one to action: ~ murder.