Today's AWAD is:

sororal (suh-ROR-uhl) adjective

Of or pertaining to a sister; sisterly.

[From Latin soror (sister). Ultimately from Indo-European root swesor- (sister) that is also the source of words cousin and sister, and words for sister in other languages such as French soeur, German Schwester, and Dutch zuster.]

Fraternal is the male equivalent of this term.

The fastest way to become sororal if you're a girl without a sister is to join a sorority. Here's a list of choices:

http://greekpages.com/org/