Ermentraut (variants include Irmentraut, Ermantraut, Ehrmantraut and Ehrmanntraut) is a rare German surname.
Further Americanized variant spellings include Ermentrout, Armentrout, Armintrout, Armantrout and Armontrout.
The derivation of German surnames from feminine given names is unusual, and at least the name Irmtraut, but possibly also the Ermentraut varieties, is instead derived from the von Irmtraut (von Ermetrode) family, members of the German lower nobility, first recorded in 1215.
The toponym Ermetrode (Irmtraut) is thus from ermet "poverty" (modern Armut) and rode "clearing", referring to a patch of poor farmland.
The presence of the surname in America is recorded for 1739, with the arrival in Philadelphia of one Anna Elizabeth Ermentraudt (née Hain).