Is a person's mother's aunt from among those to who marriage is prohibited?
Is my mother's aunt i.e. my maternal grandmother's sister, from among those to who marriage is prohibited? Does it make a difference whether or not she is my grandmother's full sister?
It is established in Islamic law that women to who marriage is prohibited for reasons of blood relations or relations through marriage include descendants and ancestors if they are once removed. These include paternal and maternal aunts, whether they are one's paternal or maternal aunts. The same prohibition applies to both a mother's and father's sisters and on up due to the words of Allah the Almighty Who says,
Prohibited to you (for marriage) are:--Your mothers, daughters, sisters; father's sisters, mother's sisters … [An-Nisaa`, 23]
This is because there is a consensus that the words 'father's sisters' includes a father's sister and a grandfather's sister no matter how high up. And the words 'mother's sister' include a mother's sister and a grandmother's sister no matter how high up (Family Law by Mohammed Mohyi Ad-Deen Abdul-Hamid. Published by Dar Al-Kitab Al-Araby, p. 45)
It is prohibited for a person to marry his mother's aunt i.e. his maternal grandmother's sister (whether or not she is a full sister) and therefore such a union is impermissible.
Allah the Almighty knows best.