A frister serves both as a friend and a sister. This word is most commonly used between twins, for they are usually incredibly close and are both friends and sisters. A frister is the ultimate companion who you may share inside jokes with, make lunches for, and watch ridiculous movies with.
Hey frister lets go catch an uber ridiculous movie, I'll make you a nice lunch with a home made granola bar in it.
Making a fist then bumping knuckles with another person in a sign of friendship or kinship. Usually reserved as a farewell but can also be used to commemorate something good that just happened or as a sign of agreement.
He dropped me off at my car, I leaned in for a hug and he gave me a fistle instead.