excursion vs field trip

excursion and field trip both are nouns.

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

As nouns, field trip is a hyponym of excursion; that is, field trip is a word with a more specific, narrower meaning than excursion:

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

Other hyponyms of excursion include airing.

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