footbridge vs gangplank

footbridge and gangplank both are nouns.

Word	Noun	Adjective	Verb	Adverb
footbridge	Yes	No	No	No
gangplank	Yes	No	No	No

As nouns, gangplank is a hyponym of footbridge; that is, gangplank is a word with a more specific, narrower meaning than footbridge:

Other hyponyms of footbridge include gangboard, gangway, jet bridge.

footbridge (noun)	gangplank (noun)
a bridge designed for pedestrians	a temporary bridge for getting on and off a vessel at dockside