Definition of "SI"

SI

proper noun
1. Initialism of Smithsonian Institution.
2. International System of Units
noun
countable and uncountable, plural SIs
1. (electronics) Initialism of signal integrity.
2. (technology) Initialism of systems integration.
3. Initialism of self-injury.
4. (fandom slang) Initialism of self-insertion. (of the author into fan fiction)
5. (mechanical engineering) Initialism of spark ignition.
6. Initialism of supporting information.
7. Initialism of special intelligence.
8. (finance) Initialism of systematic internaliser.
9. Initialism of swarm intelligence.
10. Initialism of synthetic intelligence.
11. (UK, Canada, Australia, law) Initialism of statutory instrument.
  Quotations
  The scope of SIs varies greatly, from the technical (e.g. to set or vary the dates on which different provisions of an Act will come into force, to change the levels of fines or penalties for offences or to make consequential and transitional provisions) to the much wider-ranging, such as filling out the broad provisions in Acts.
  2016 December 15, Richard Kelly, Statutory Instruments‎, House of Commons Library Briefing Paper 6509, archived from the original on 7 January 2022, page 1
12. Initialism of subinspector. (of police, etc)
adjective
not comparable
1. (anatomy, medicine) Initialism of sacroiliac.