coccyx

UK: /ˈkɒksɪks/ US: /ˈkɑksɪks/ ,(kok′siks)

Inflections of 'coccyx' (n): npl: coccyges

WordReference Random House Learner's Dictionary of American English © 2025

coc•cyx /ˈkɑksɪks/   n. [countable] , pl. coc•cy•ges 

/kɑkˈsaɪdʒiz, ˈkɑksɪˌdʒiz/.  
1. Anatomy a triangular bone at the lower end of the spinal column;
   tailbone.

WordReference Random House Unabridged Dictionary of American English © 2025

coc•cyx  (kok′siks), n., pl. coc•cy•ges 

(kok sī′jēz, kok′si jēz′). 
1. Anatomy a small triangular bone forming the lower extremity of the spinal column in humans, consisting of four ankylosed rudimentary vertebrae. See diag. under spinal column. 
2. a corresponding part in certain animals.

• Greek kókkyx cuckoo, from its resemblance to a cuckoo's beak
• Neo-Latin
• 1605–15;

coc•cyg•e•al  (kok sij′ē əl), adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

coccyx / ˈkɒksɪks/ noun ( coccyges / kɒkˈsaɪdʒiːz/)

1. a small triangular bone at the end of the spinal column in humans and some apes, representing a vestigial tail

Etymology: 17th Century: from New Latin, from Greek kokkux cuckoo, of imitative origin; from the likeness of the bone to a cuckoo's beak

coccygeal / kɒkˈsɪdʒɪəl/, coccygian / kɒkˈsɪdʒɪən/ adjective