Helpmate, n.
Etymology: [A corruption of the help meet for him of Genesis ii. 18.Fitzedward Hall.]
A helper; a companion; specifically, a wife. In Minorca the ass and the hog are common helpmates, and are yoked together in order to turn up the land. Pennant. A waiting woman was generally considered as the most suitable helpmate for a parson. Macaulay.
Shades of meaning
Fernald has no entry of its own for helpmate; he lists it under associate.
He lists it without comment; the entries above explain its neighbors.