June 21 vs summer solstice

June 21 and summer solstice both are nouns.

Word	Noun	Adjective	Verb	Adverb
June 21	Yes	No	No	No
summer solstice	Yes	No	No	No

As nouns, June 21 and summer solstice are synonyms defined as:

June 21 and summer solstice: June 21, when the sun is at its northernmost point

Other synonyms of June 21 include midsummer.

June 21 (noun)	summer solstice (noun)
June 21, when the sun is at its northernmost point	June 21, when the sun is at its northernmost point