Левит 18:12

Marriage or conjugal intercourse with the sister of either father or mother (i.e., with either the paternal or maternal aunt) was prohibited, because she was the blood-relation of the father or mother. שׁאר = בּשׂר שׁאר (Lev 18:6, as in Lev 20:19; Lev 21:2; Num 27:11), hence שׁארה, blood-relationship (Lev 18:17).

Here is, I. A general law against all conformity to the corrupt usages of the heathen (Lev 18:1-5). II. Particular laws, 1. Against incest (Lev 18:6-18). 2. Against beastly lusts, and barbarous idolatries (Lev 18:19-23). III. The enforcement of these laws from the ruin of the Canaanites (Lev 18:24-30).

18:12-13 your father’s sister . . . mother’s sister: These actions would dishonor your father or mother.