From Longman Dictionary of Contemporary Englishcoccyxcoc‧cyx /ˈkɒksɪks $ ˈkɑːk-/ noun (plural coccyxes or coccyges /kɒkˈsaɪdʒiːz $ ˈkɑːksə-/) [countable] technical HBHthe small bone at the bottom of your spine SYN tailbone
Examples from the Corpus
coccyx• Too much to expect a new pair of arms to grow out of her ribs, or her coccyx to elongate so enormously.• Pain like this after a fall on the coccyx.Origin coccyx (1500-1600) Modern Latin Greek kokkyx “cuckoo”; because it looks like a cuckoo's beak 