idea vs reckoning

idea and reckoning both are nouns.

Word	Noun	Adjective	Verb	Adverb
idea	Yes	No	No	No
reckoning	Yes	No	No	No

As nouns, reckoning is a hypernym of idea; that is, reckoning is a word with a broader meaning than idea:

Other hypernyms of idea include calculation, computation, figuring.

idea (noun)	reckoning (noun)
the content of cognition; the main thing you are thinking about	the act of counting; reciting numbers in ascending order
your intention; what you intend to do	problem solving that involves numbers or quantities
an approximate calculation of quantity or degree or worth	a bill for an amount due
a personal view
(music) melodic subject of a musical composition