pen vs playpen

pen and playpen both are nouns.

Word	Noun	Adjective	Verb	Adverb
pen	Yes	No	Yes	No
playpen	Yes	No	No	No

As nouns, pen and playpen are synonyms defined as:

pen and playpen: a portable enclosure in which babies may be left to play

pen (noun)	playpen (noun)
female swan	a portable enclosure in which babies may be left to play
a writing implement with a point from which ink flows
an enclosure for confining livestock
a correctional institution for those convicted of major crimes
a portable enclosure in which babies may be left to play

pen (verb)	playpen (verb)
produce a literary work