The ultra important, high falutin, and just all around annoying sister of your spouse. She will not be at your wedding because she has more important things to do, and if by chance she shows up, she'll ruin it. She's your mother-in-law's teammate and soldier.
The ideal sister-in-law is one that resides six feet below the ground in a cemetery, right next to the ideal mother-in-law.
by Xxxxxxxxfanboyxxxxxxxxxx February 01, 2021
My sister-in-law ruined my wedding by demanding I pay for her wedding and starting a family fight. Of course my mother-in-law took her side.
by Xxxxxxxxfanboyxxxxxxxxxx November 18, 2020
Standard Sister-in-Law Unit
noun
*| \ ˈsta-ndərd ˈsi-stər-in-ˌlȯ yü-nət *
Abbreviation: SSILU
Symbol: 𝓢 or SIL
Definition:
An unofficial unit of mass equal to 300 pounds (136.08 kilograms), used to simulate high-risk, real-world human load scenarios in mechanical, structural, and transportation systems. The SSILU is commonly applied to test the failure thresholds of furniture, vehicle seats, elevators, bicycles, airline cabins, and public patience.
Etymology:
Originated in post-war American slang, the term is derived from the stereotype of a loud, heavyset female relative—often portrayed as emotionally volatile and structurally compromising—whose presence tests both family dynamics and infrastructure load-bearing capacity. While non-literal, the “sister-in-law” archetype evokes maximum physical and psychological mass concentration in civilian environments.
Technical Classification:
Measurement Type: Anthropomorphic Load Unit
Mass: 300 lbs (≈ 136.08 kg)
Field Use: Structural stress testing, emergency engineering simulation
Design Benchmark: Most consumer goods are not rated past 0.8 SSILU
noun
*| \ ˈsta-ndərd ˈsi-stər-in-ˌlȯ yü-nət *
Abbreviation: SSILU
Symbol: 𝓢 or SIL
Definition:
An unofficial unit of mass equal to 300 pounds (136.08 kilograms), used to simulate high-risk, real-world human load scenarios in mechanical, structural, and transportation systems. The SSILU is commonly applied to test the failure thresholds of furniture, vehicle seats, elevators, bicycles, airline cabins, and public patience.
Etymology:
Originated in post-war American slang, the term is derived from the stereotype of a loud, heavyset female relative—often portrayed as emotionally volatile and structurally compromising—whose presence tests both family dynamics and infrastructure load-bearing capacity. While non-literal, the “sister-in-law” archetype evokes maximum physical and psychological mass concentration in civilian environments.
Technical Classification:
Measurement Type: Anthropomorphic Load Unit
Mass: 300 lbs (≈ 136.08 kg)
Field Use: Structural stress testing, emergency engineering simulation
Design Benchmark: Most consumer goods are not rated past 0.8 SSILU
“She hit the fitting room like a breaching whale—1 Standard Sister-in-Law Unit (SSILU) 300lbs in full stride, swatting children aside and hollering ‘THESE SIZES RUN SMALL!!! while nearby store associates quietly begged for a swift death
by Ludwig Von Snooterman June 07, 2025