עֶרְוַ֥ת אֲחִֽי־אָבִ֖יךָ לֹ֣א תְגַלֵּ֑ה אֶל־אִשְׁתּוֹ֙ לֹ֣א תִקְרָ֔ב דֹּדָֽתְךָ֖ הִֽוא׃ (ס)
Thou shalt not uncover the nakedness of thy fathers brother, thou shalt not approach to his wife: she is thine aunt.
Read kabbalistic (mystical) interpretation of Leviticus 18:14: and classical mystical sources.