sd

sd is the alternative letter-case form of SD.

Proper noun capitalized: SD

(abbreviation, initialism, postal) Initialism of South Dakota: a state of the United States.
(abbreviation, initialism, uncountable) Initialism of Secure Digital: a non-volatile memory card format developed for use in portable devices.
- I had responsibility for safely extracting SD cards and manually uploading footage onto the server.2023, Martin MacInnes, In Ascension, Atlantic Books, page 44

SD (plural SDs)

(abbreviation, initialism) Initialism of school district.
(abbreviation, initialism) Initialism of sheriff's department.
(abbreviation, initialism) Initialism of standard deviation.
(abbreviation, initialism) Initialism of self-destruct.
(abbreviation, initialism) Initialism of segmental duplication.
- We estimated that the following percentage of elements were correctly assembled: 95.4% of alpha satellites; 91.5% of human satellites 2 and 3; 97.7% of segmental duplications (SDs); 94.3% of variable number tandem repeats (VNTRs); 94.2% of short tandem repeats (STRs); and 98.8% of all human...2023 May 11, Wen-Wei Liao, Mobin Asri, Jana Ebler, et al., “A draft human pangenome reference”, in Nature, volume 617, →DOI, page 313
(abbreviation, initialism, relationships) Initialism of sugar daddy

SD (uncountable)

(abbreviation, initialism) Initialism of standard definition (“typically 640×480 pixels”).

plural	sds
plural	SDs

What is sd the alternative letter-case form of?: Sd is the alternative letter-case form of SD.
What part of speech is sd?: Sd can be a proper noun or a noun.

Adapted from Wiktionary: sd (page history and authors); SD (page history and authors). Text available under the Creative Commons Attribution-ShareAlike 4.0 license. Word.ws reformatted the entry and added links. Wiktionary data of 2026-09-02.

Last updated: 2026-09-02

Cite this entry: “sd.” Word.ws, https://word.ws/sd. Based on Wiktionary, CC BY-SA 4.0.