The correct option is D Polyandry
One word for the phrase 'The custom of having more than one husband at the same time' is Option B, 'Polyandry'. Option A 'Polygamy' is the practice of getting married more than once. Option C 'Debauchery' is excessive indulgence in alcohol and drugs. Option D 'Bigamy' is. offense of marrying someone who is already married. Thus, the options A, C and D are incorrect and the correct option is Option B, Polyandry.