extradural vs epidural

extradural is not a noun while epidural is a noun.

Word	Noun	Adjective	Verb	Adverb
extradural	No	Yes	No	No
epidural	Yes	Yes	No	No

As adjectives, extradural and epidural are synonyms defined as:

extradural (noun)	epidural (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

extradural (adjective)	epidural (adjective)
on or outside the dura mater	on or outside the dura mater