From Longman Dictionary of Contemporary Englishtailbonetail‧bone /ˈteɪlbəʊn $ -boʊn/ noun [countable] HBHthe small bone at the bottom of your spine SYN coccyx
Examples from the Corpus
tailbone• 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. 