endeavor vs be at pains

endeavor is a noun but be at pains is not a noun.

Word	Noun	Adjective	Verb	Adverb
endeavor	Yes	No	Yes	No
be at pains	No	No	Yes	No

As verbs, be at pains is a hyponym of endeavor; that is, be at pains is a word with a more specific, narrower meaning than endeavor:

Other hyponyms of endeavor include struggle, take pains, buck.

endeavor (noun)	be at pains (noun)
earnest and conscientious activity intended to do or accomplish something
a purposeful or industrious undertaking (especially one that requires effort or boldness)

endeavor (verb)	be at pains (verb)
attempt by employing effort	try very hard to do something