tailbone
From Longman Dictionary of Contemporary EnglishRelated topics: Humantailbonetail‧bone /ˈteɪlbəʊn $ -boʊn/ noun [countable] HBHthe small bone at the bottom of your spine SYN coccyxExamples from the Corpustailbone• Somehow he had landed on his backside and then had felt his tailbone knock the earth harder than was safe.• His voice was so low that it tickled my tailbone.