Wilmot. When I was doing research on my ancestors in Cornwall, I came across TONS of Wilmots, Wilmotts, Willmots, etc; all female. And although
Wilmot isn't exactly a popular name on either gender I'd say that most people would assume a
Wilmot is male.
Also I think
Christian was originally feminine? And
Julian? Or at least more unisex than they are now. I remember reading about some medieval Christians and Julians who were women.