What is sisterly?

The 'love' between two sisters.

Normally sarcastic-

Y: Yup, my sister told me to jump off a cliff today..
N: Just 'sisterly love'.

sisterly - meme gif

A friend who displays affection and kindness in a way your own sister would if she really cared about anyone but herself.

Jay was being super sisterly by supporting my decision to get an abortion.