Sis is short for sister and also an informal way to address a female sibling or a close friend.
When you call someone "sis", it's like saying "sister" but without the formal connotation. You might use it with your little sister, but also with a friend who feels like a sister to you. If you're chatting with friends online and one of them says "What's up sis?", they're probably just being casual and friendly.
How common is "sis"?
Word sis is considered rare in modern English. It appears most frequently in fiction texts and less often in other writings.
Definitions
noun
A daughter of the same parents as another person; a female sibling.
Example: My sister is always driving me crazy.
A female member of a religious order; especially one devoted to more active service; (informally) a nun.
Example: Michelle left behind her bank job and became a sister at the local convent.
Any butterfly in the genus Adelpha, so named for the resemblance of the dark-colored wings to the black habit traditionally worn by nuns.
A senior or supervisory nurse, often in a hospital.
Any woman or girl with whom a bond is felt through common membership of a race, profession, religion or organization, such as feminism.
Example: Connie was very close to her friend Judy and considered her to be her sister.
(sometimes capitalized) A black woman.
A form of address to a woman.
Example: What’s up, sister?
A woman, in certain labour or socialist circles; also as a form of address.
Example: Thank you, sister. I would like to thank the sister who just spoke.
An entity that has a special or affectionate, non-hierarchical relationship with another.
Example: sister city
A node in a data structure that shares its parent with another node.
(usually attributively) Something in the same class.
