Gentile characters are usually flat and stock — the cruel landlord, the boorish peasant — and the defining characteristic of the gentile female is a straightforward binary: either she is a temptress or she is not.
It’s along this line that the shiksa semantically splits: (1) the non-tempting gentile woman, whose relationship to the Jew is often of an incidental sort, like that of a maid or neighbor, and who, if she’s described at all, is usually a hag; and (2) the tempting and by-definition forbidden seductress (though “seductress” implies a proactivity that isn’t always or even usually the case: the shiksa need not make any sexual overtures or come-ons beyond her simply existing and being visible, which, granted, would be considered by many in the are pejorative, but in different ways and of different intensities: one personifies forbidden pleasure, sharply reflecting the guilt and frustration of the tempted; the other is blandly derogatory, almost below concern. Bialik’s 1909 novella : there’s Shakoripinshchika, an ugly and violent old woman, and her beautiful granddaughter Marinka, who has a touching but secret childhood romance with the Jewish neighbor, Noah.
In Israel, where there are not that many non-Jewish women around to apply it to, “shiksa” is now used pretty much exclusively by the ultra-Orthodox to describe/insult a non-religious Jewish woman.
Two Israeli comedians (in Haredi costume) satirized this last year in a song.