sister

As a noun sister

is title of respect for an adult female member of a religious or fraternal order.

As an adjective sisterless is

without a sister.

As nouns the difference between sister and sistergirl

is that sister is a daughter of the same parents as another person; a female sibling while sistergirl is sister, girlfriend (as a familiar term of address between women).

As a verb sister

is to strengthen (a supporting beam) by fastening a second beam alongside it.

As nouns the difference between sister and sororate

is that sister is title of respect for an adult female member of a religious or fraternal order while sororate is the custom of the marriage of a man to the sister of his wife, usually after the wife has died.