Grammar gripe . . .

. . . or one of these days, I'm gonna murder my milon.  Why is it that a Hebrew-English milon/dictionary never gives the feminine form of a masculine noun?  If I hadn't spent several years in Ulpan Hebrew classes, I would have no idea that a religious woman is called datit, not datiyah.  And I only learned a few weeks ago that a female soldier is called a chayelet, not a chayalah, as I had thought.  How is one supposed to tell which way to modify a masculine noun?  In all seriousness, is there some secret to this aspect of Hebrew dikduk/grammar that I've never learned?  If so, please enlighten me in the comments.  Thanks for your help.