mercurial ointment vs balm

mercurial ointment and balm both are nouns.

Word	Noun	Adjective	Verb	Adverb
mercurial ointment	Yes	No	No	No
balm	Yes	No	No	No

As nouns, balm is a hypernym of mercurial ointment; that is, balm is a word with a broader meaning than mercurial ointment:

mercurial ointment: an ointment containing mercury
balm: semisolid preparation (usually containing a medicine) applied externally as a remedy or for soothing an irritation

Other hypernyms of mercurial ointment include ointment, salve, unction, unguent.

mercurial ointment (noun)	balm (noun)
an ointment containing mercury	semisolid preparation (usually containing a medicine) applied externally as a remedy or for soothing an irritation
	any of various aromatic resinous substances used for healing and soothing