Biro vs ballpen

Biro and ballpen both are nouns.

Word	Noun	Adjective	Verb	Adverb
Biro	Yes	No	No	No
ballpen	Yes	No	No	No

As nouns, Biro and ballpen are synonyms defined as:

Biro and ballpen: a pen that has a small metal ball as the point of transfer of ink to paper

Other synonyms of Biro include ballpoint, ballpoint pen.

Biro (noun)	ballpen (noun)
a pen that has a small metal ball as the point of transfer of ink to paper	a pen that has a small metal ball as the point of transfer of ink to paper