historionomer
/hɪˌstɒrɪˈɒnəmə/ /hɪˌstɔːrɪˈɒnəmə/ /ˌhɪstɒrɪˈɒnəmə/rare
noun
A student of or expert in the principles which regulate the course of history.
Origin
Mid 19th century; earliest use found in James Russell Lowell (1819–1891), author and diplomat. Apparently from ancient Greek ἱστορία history + -nomer. With later use compare German Historionom.