felt-tipped pen vs felt-tip pen

felt-tipped pen and felt-tip pen both are nouns.

Word	Noun	Adjective	Verb	Adverb
felt-tipped pen	Yes	No	No	No
felt-tip pen	Yes	No	No	No

As nouns, felt-tipped pen and felt-tip pen are synonyms defined as:

felt-tipped pen and felt-tip pen: a pen with a writing tip made of felt (trade name Magic Marker)

Other synonyms of felt-tipped pen include felt tip, Magic Marker.

felt-tipped pen (noun)	felt-tip pen (noun)
a pen with a writing tip made of felt (trade name Magic Marker)	a pen with a writing tip made of felt (trade name Magic Marker)