felt tip vs pen

felt tip and pen both are nouns.

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

As nouns, pen is a hypernym of felt tip; that is, pen is a word with a broader meaning than felt tip:

felt tip (noun)	pen (noun)
a pen with a writing tip made of felt (trade name Magic Marker)	female swan
	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

felt tip (verb)	pen (verb)
	produce a literary work