ischial bone vs ischium

ischial bone and ischium both are nouns.

Word	Noun	Adjective	Verb	Adverb
ischial bone	Yes	No	No	No
ischium	Yes	No	No	No

As nouns, ischial bone and ischium are synonyms defined as:

ischial bone and ischium: one of the three sections of the hipbone; situated below the ilium

Other synonyms of ischial bone include os ischii.

ischial bone (noun)	ischium (noun)
one of the three sections of the hipbone; situated below the ilium	one of the three sections of the hipbone; situated below the ilium