S21 or S-21 may refer to:
Automobiles
Aviation
- De Schelde S.21, a proposed Dutch fighter
- Rans S-21 Outbound, an American homebuilt aircraft
- SIAI S.21, an Italian racing flying boat
- Sikorsky S-21, the first four-engine aircraft in the world
- Short S.21 Maia, a British flying boat mother ship
- Spalinger S.21, a Swiss training glider
- Sukhoi-Gulfstream S-21, a proposed American business jet
- Sunriver Airport in Sunriver, Oregon
Rail and transit
Lines
- S21 (Berlin), a planned S-Bahn line in Berlin, Germany
- S21 (RER Fribourg), an S-Bahn line in the canton of Freibourg, Switzerland
- S21 (ZVV), an S-Bahn line in the cantons of Zürich and Zug in Switzerland
- Stuttgart 21, a transportation and urban project in Stuttgart, Germany
- S21, a line of the Hamburg S-Bahn
Stations
- Ginzan Station, in Niki, Hokkaidō, Hokkaidō, Japan
- Moto-Yawata Station, in Ichikawa, Chiba, Japan
- Shin-Fukae Station, in Osaka, Japan
- Tokushige Station, in Midori-ku, Nagoya, Aichi, Japan
Roads
- S21 Guangzhou–Huidong Expressway, China
- County Route S21 (California), United States
Submarines
- ARA Santa Fe (S-21), of the Argentine Navy
- Brazilian submarine Tonelero (S21)
- HMS Onyx (S21), of the Royal Navy
- INS Kalvari (S21), of the Indian Navy
- INS Karanj (S21), of the Indian Navy
- USS S-21 (SS-126), of the United States Navy
Other uses
- 40S ribosomal protein S21
- British NVC community S21, a swamps and tall-herb fens community in the British National Vegetation Classification system
- Forward voltage gain or transmission coefficient of a two-port network
- S-21: The Khmer Rouge Killing Machine, a 2003 documentary film
- S21: When using do not smoke, a safety phrase
- Samsung Galaxy S21, a series of smartphones
- Security Prison 21, now the Tuol Sleng Genocide Museum in Cambodia
- Serbia 21, a political organization in Serbia
- s21 notice, in England & Wales, from a landlord instructing tenants to leave
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Topics referred to by the same termThis disambiguation page lists articles associated with the same title formed as a letter–number combination.If an internal link led you here, you may wish to change the link to point directly to the intended article. Category: