pi-meson vs pion

pi-meson and pion both are nouns.

Word	Noun	Adjective	Verb	Adverb
pi-meson	Yes	No	No	No
pion	Yes	No	No	No

As nouns, pi-meson and pion are synonyms defined as:

pi-meson and pion: a meson involved in holding the nucleus together; produced as the result of high-energy particle collision

pi-meson (noun)	pion (noun)
a meson involved in holding the nucleus together; produced as the result of high-energy particle collision	a meson involved in holding the nucleus together; produced as the result of high-energy particle collision