sphere vs realm

sphere and realm both are nouns.

Word	Noun	Adjective	Verb	Adverb
sphere	Yes	No	No	No
realm	Yes	No	No	No

As nouns, realm is a hyponym of sphere; that is, realm is a word with a more specific, narrower meaning than sphere:

sphere (noun)	realm (noun)
any spherically shaped artifact	a knowledge domain that you are interested in or are communicating about
a particular aspect of life or activity	the domain ruled by a king or queen
the geographical area in which one nation is very influential	a domain in which something is dominant
the apparent surface of the imaginary sphere on which celestial bodies appear to be projected
a solid figure bounded by a spherical surface (including the space it encloses)
a three-dimensional closed surface such that every point on the surface is equidistant from the center
a particular environment or walk of life