Select the option that can be used as a one-word substitute for the given group of words.
A woman having more than one husband at the same time

The correct option is Polyandry.

Explanation:
Let us analyze the meanings of all the options to determine the correct one-word substitution for "A woman having more than one husband at the same time":

1. Polyandry: A form of polygamy in which a woman has more than one husband simultaneously. This matches the given definition exactly.

2. Endogamy: The practice or custom of marrying within a specific social group, religious community, or ethnic group.

3. Polymathy: The condition or quality of having wide-ranging knowledge or learning across many different subjects.

4. Monogamy: The practice or state of being married to or in a relationship with only one person at a time.

Thus, the appropriate one-word substitute for the given phrase is Polyandry.