field trip vs excursion

field trip and excursion both are nouns.

Word	Noun	Adjective	Verb	Adverb
field trip	Yes	No	No	No
excursion	Yes	No	No	No

As nouns, excursion is a hypernym of field trip; that is, excursion is a word with a broader meaning than field trip:

field trip: a group excursion (to a museum or the woods or some historic place) for firsthand examination
excursion: a journey taken for pleasure

Other hypernyms of field trip include expedition, jaunt, junket, outing, pleasure trip, sashay.

field trip (noun)	excursion (noun)
a group excursion (to a museum or the woods or some historic place) for firsthand examination	a journey taken for pleasure
	wandering from the main path of a journey