[{"Bold_text": "noun", "List Items": ["the back of a horse.", "Geology.a low, natural ridge of sand or gravel; an esker.Compare hogback ."]}, {"Bold_text": "adverb", "List Items": ["on horseback:to ride horseback."]}, {"Bold_text": "adjective", "List Items": ["made or given in a casual or speculative way; approximate or offhand:a horseback estimate on the construction costs."]}]