Mantell man·tell US/mæˈntɛl/ uncommon noun 1. English geologist remembered as the first person to recognize that dinosaurs were reptiles (1790-1852) SynonymsGideon Algernon Mantell Related words Broader terms geologist WordNet 2.1 (Princeton University). CMU Pronouncing Dictionary. WordNet 2.1 Copyright Princeton University. All rights reserved.