Sister-Mom 

A sister who by blood is a sibling, but happens to play the role of Mother figure as well. (Sibling Co-Parenting)

This can occur for a variety of reasons such as cultural background, parents work schedules or simply having a large family.

Example 1: My sister-mom has helped me raise my grades, helped me focus on my future and is also my best friend.

Example 2: Teacher - "Hey, is that your mom over there? Is she picking you up from school today?"
Student: "Oh, no, that's my sister-mom."
Teacher: *confused look*
Student: "Well, she is my sister, but she also acts like my mom"

Sister-Mom by WordWatch January 20, 2018

sister-mom 

When someone's mom looks so young she could be their sister.

Jenny is coming to the party and she is bringing her sister-mom. I saw Chris shopping with his sister-mom.

sister-mom by jillyjillz May 2, 2011

Sister-mom 

When your dad has sex with a woman and said woman has a girl for a child. Then the dad fucks the daughter and you are born. Motha fuckin sista mom

guy #1 "Dude your mom is hot"
guy #2 "That's my sister"
guy #1 "Oh shit, you got a sister-mom"

Sister-mom by zeilgarsiulgfiSDoiuSEibugsEigu February 24, 2012

Sister Mom 

A mother to one or more children with a best friend who may or may not also have children. They do not live together but can call on each other at any given point to step in. They have complete confidence that other mom will do as great or better as they can.

"Her sister mom picked up the children and took the kids to practice while she was stuck at work"

Sister Mom by MomInDe May 9, 2022

National Threesome with your Sister and Mom day 

This holiday of joy is celebrated on 25th December. Have fun people!

Jeff: what you doing today bro?
Bro: What do you think it’s National Threesome with your Sister and Mom day

National Threesome with your Sister and Mom day by Hikari 𓆏#696 October 14, 2021

Sister moment here 

Something you say when you and your sister are on the same page or wavelength in the moment.

Both:"OMG.Sister moment here"

Sister moment here by Stormzroundkorner February 27, 2019

sistertommy 

best and hottest mutual u could ever ask for

sistertommy is so hot i want to kiss them rn

sistertommy by lmaookissmyass July 8, 2021