midsummer vs June 21

midsummer and June 21 both are nouns.

Word	Noun	Adjective	Verb	Adverb
midsummer	Yes	No	No	No
June 21	Yes	No	No	No

As nouns, midsummer and June 21 are synonyms defined as:

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

Other synonyms of midsummer include summer solstice.

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