sacral vertebra vs vertebra

sacral vertebra and vertebra both are nouns.

Word	Noun	Adjective	Verb	Adverb
sacral vertebra	Yes	No	No	No
vertebra	Yes	No	No	No

As nouns, vertebra is a hypernym of sacral vertebra; that is, vertebra is a word with a broader meaning than sacral vertebra:

sacral vertebra: one of 5 vertebrae in the human spine that fuse in the adult to form the sacrum
vertebra: one of the bony segments of the spinal column

sacral vertebra (noun)	vertebra (noun)
one of 5 vertebrae in the human spine that fuse in the adult to form the sacrum	one of the bony segments of the spinal column