epidural vs regional anesthesia

epidural and regional anesthesia both are nouns.

Word	Noun	Adjective	Verb	Adverb
epidural	Yes	Yes	No	No
regional anesthesia	Yes	No	No	No

As nouns, regional anesthesia is a hypernym of epidural; that is, regional anesthesia is a word with a broader meaning than epidural:

epidural: regional anesthesia resulting from injection of an anesthetic into the epidural space of the spinal cord; sensation is lost in the abdominal and genital and pelvic areas; used in childbirth and gynecological surgery
regional anesthesia: loss of sensation in a region of the body produced by application of an anesthetic agent to all the nerves supplying that region (as when an epidural anesthetic is administered to the pelvic region during childbirth)

Other hypernyms of epidural include regional anaesthesia.

epidural (noun)	regional anesthesia (noun)
regional anesthesia resulting from injection of an anesthetic into the epidural space of the spinal cord; sensation is lost in the abdominal and genital and pelvic areas; used in childbirth and gynecological surgery	loss of sensation in a region of the body produced by application of an anesthetic agent to all the nerves supplying that region (as when an epidural anesthetic is administered to the pelvic region during childbirth)

epidural (adjective)	regional anesthesia (adjective)
on or outside the dura mater