felt-tip pen vs felt tip

felt-tip pen and felt tip both are nouns.

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

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

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

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

felt-tip pen (noun)	felt tip (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)