1590s, "fact or quality of being improbable;" see improbable + -ity. Meaning "an instance of something improbable" is from 1610s.
the improbability of such rare coincidences
impossibility should never be confused with improbability
imprevisible
imprimatur
imprint
imprison
imprisonment
improbability
improbable
improbity
imprompt
impromptitude
impromptu
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