Rashi on Leviticus 21:7/רש"י על ויקרא כ״א:ז׳

1זנה is a woman who had sexual intercourse with an Israelite who is forbidden to her as a husband, for instance, with those whom she may not marry under the penalty of excision, or a Gibeonite or a ממזר (that is, a man born from the union of a couple who are liable to excision for such a union) (cf. Sifra, Emor, Chapter 1 7; Yevamot 61b).

2חללה — This is a woman born from a marriage which is forbidden to the priesthood alone (Kiddushin 77a), e. g., the daughter of a widow and a high priest, or the daughter of a divorced woman [or one released from levirate marriage by the appropriate ceremony (cf. Deuteronomy 25:9)] and an ordinary priest. So also it denotes a woman who became profaned in respect to the priesthood (who lost the right of marrying a priest) through her having previously entered into a union with one of those priests a marriage with whom comes under the term: "marriages forbidden to the priesthood alone”.