Coccyx as a noun is the final fused vertebrae at the base of the spine. while Sacrum as a noun is a large triangular bone located at the base of the spine between the two hipbones of pelvis and formed from fused vertebrae.
Part of speech: noun
Definition: The final fused vertebrae at the base of the spine.
Part of speech: noun
Definition: A large triangular bone located at the base of the spine between the two hipbones of pelvis and formed from fused vertebrae.
We hope you now know whether to use Coccyx or Sacrum in your sentence.