guava vs Psidium guajava

guava and Psidium guajava both are nouns.

Word	Noun	Adjective	Verb	Adverb
guava	Yes	No	No	No
Psidium guajava	Yes	No	No	No

As nouns, guava and Psidium guajava are synonyms defined as:

guava and Psidium guajava: small tropical American shrubby tree; widely cultivated in warm regions for its sweet globular yellow fruit

Other synonyms of guava include guava bush, true guava.

guava (noun)	Psidium guajava (noun)
tropical fruit having yellow skin and pink pulp; eaten fresh or used for e.g. jellies	small tropical American shrubby tree; widely cultivated in warm regions for its sweet globular yellow fruit
small tropical American shrubby tree; widely cultivated in warm regions for its sweet globular yellow fruit
small tropical shrubby tree bearing small yellowish fruit