underestimation vs underreckoning

underestimation and underreckoning both are nouns.

Word	Noun	Adjective	Verb	Adverb
underestimation	Yes	No	No	No
underreckoning	Yes	No	No	No

As nouns, underestimation and underreckoning are synonyms defined as:

underestimation and underreckoning: an estimation that is too low; an estimate that is less than the true or actual value

Other synonyms of underestimation include underestimate, underrating.

underestimation (noun)	underreckoning (noun)
an estimation that is too low; an estimate that is less than the true or actual value	an estimation that is too low; an estimate that is less than the true or actual value