It depends on what the name means. The ending -iel often means 'maiden', but not here. In this case Undómiel means evenstar, not even-maiden. I keep forgetting this, as I usually think of Arwen when I hear/see Undómiel and therefore see it is a feminine name.
It comes from Undómë
, meaning twilight/evening, and -el
, meaning star. (If I'm not horribly mistaken.)
Here is an nice article about elven names and how they are made.
Now We Have All Got Elvish Names