SIS 

Secret Internet Shorty, an acronym used to describe pictures of a guys dick but using angles or photoshop to make appear significantly bigger than it really is.

Look at this dickture I just got from this guy! I know know for a fact he is a SIS!

SIS by IamIwhoIam August 20, 2011

SIS 

Due to the vast majority of lies which happens every time a person types 'LOL' in texting or the internet, SIS (Smile in Silence) is a much more proper use in times when one does not actually laugh when typing 'LOL'. Though, this may suggest that the person is not as fun as he did not actually laugh.

A: Yo, B, I just tried walking thru at a drive thru.
B: LOL, what happened?
A: B, stop lying bro, don't tell me you actually laughed at that message. SIS
B: Jeez, such a stickler...So what happened?
A: They told me that they only viewed car owners as acceptable customers.
B: SIS

SIS by Shinigami Prophet July 10, 2014

Sis 

A sexual nickname between gang members.

Hey there sis.

Sis by Gang guy 254 October 14, 2016

Sis 

The ultimate friendzone

Short for sisters

1- hey

2-hey sis

Sis by Mandagrace99 November 24, 2018

sis 

The Queen Bitch Hacker

"Sis & Sabbath Own you"

sis by Sis March 8, 2003

Sis 

A word basic bitches use to get a point across.
It’s the most cringe worthy word that can be used and should be illegal in every way.

“Omg sis I just got a brand new Rolex”
“Sis hop in my fiat500 let’s go for a ride”

Sis by Shanosthetranos July 6, 2020

Sis 

A sexual nickname used by gang members

Hey sis

Sis by Gang guy 254 October 14, 2016