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anachronism
anything that is out of place in time
anon
soon; shortly
antebellum
before the war; especially before the American Civil War
antediluvian
old fashioned; before the flood
atavism
reversion to a primitive type; resemblance to a remote ancestor
augury
the art of prophecy; an omen
betimes
early; promptly; before it is too late
biennial
happening every two years
diurnal
daily; of the daytime
eon
long, indefinite period of time; thousands of years
ephemeral
short-lived; transitory
epoch
noteworthy period
generation
the period of time between the birth of one group and that of its offspring
score
twenty people or objects; twenty years
tercentenary
a period of 300 years