{{Short description|Numerical prefix meaning "ten"}} {{Other uses|Deca (disambiguation){{!}}Deca}} {{Wiktionary|deca-}} {{Wiktionary|deca-|deka-|dec-}}

'''Deca''' (and '''dec'''; sometimes '''deka''') is a common English-language numeral prefix derived from the Late Latin {{Lang|la|decas}} ("(set of) ten"), from Ancient Greek {{Lang|grc|δεκάς (dekás)}}, from {{Lang|grc|δέκα}} (déka, "ten").<ref>{{Cite book|title=Chambers Twentieth Century Dictionary|date=1979|page=332}}</ref> It is used in many words.

It is also a decimal unit prefix in the International System of Units (SI) denoting a factor of ten, with symbol '''da''' and spelled "deca" internationally{{efn|As used by the International Bureau of Weights and Measures.<ref name="bipm-spelling">[https://www.bipm.org/en/publications/si-brochure/chapter3.html ''Decimal multiples and submultiples of SI units''] {{Webarchive|url=https://web.archive.org/web/20190330005801/https://www.bipm.org/en/publications/si-brochure/chapter3.html |date=2019-03-30 }}, 2006, SI Brochure: The International System of Units (SI), 8th edition</ref>}} (or "deka" in American spelling<ref name=SP811>[http://physics.nist.gov/Pubs/SP811/sp811.html ''Guide for the Use of the International System of Units (SI)''], 1995, NIST Special Publication 811</ref>).

==SI== The prefix was a part of the original metric system in 1795. It is not in very common usage, although the decapascal is occasionally used by audiologists. The decanewton is also encountered occasionally, probably because it is an SI approximation of the kilogram-force. Its use is more common in Central Europe. In German, Polish, Czech, Slovak, and Hungarian, ''deka'' (or ''deko'') is common, and used in self-standing form, always meaning ''decagram''. A runway number typically indicates its magnetic azimuth in decadegrees.

Before the symbol as an SI prefix was standardized as ''da'' with the introduction of the International System of Units in 1960, various other symbols were more common, such as ''dk'' (e.g., UK and Austria, still common in Hungary for decagrams), ''D'' (e.g., Germany, Eastern Europe), and ''Da''. For syntactical reasons, the HP 48<!-- at least 48G/GX/G+/GII, not sure about 48S/SX-->, 49, 50 series, as well as the HP 39gII and Prime calculators use the unit prefix ''D''.<ref name="HP48_UG">{{cite book | title=HP&nbsp;48G Series – User's Guide (UG) | publisher=Hewlett-Packard | edition=8 | date=December 1994 | id=HP 00048-90126, (00048-90104) | orig-year=1993<!-- edition 1 (1993-05) --> | url=http://www.hpcalc.org/details.php?id=3937 | access-date=2015-09-06}}</ref><ref name="HP50g_UG">{{cite book | title=HP 50g graphing calculator user's guide (UG) | publisher=Hewlett-Packard | edition=1 | date=2006-04-01 | id=HP F2229AA-90006 | url=http://www.hpcalc.org/details.php?id=6512 | access-date=2015-10-10}}</ref><ref name="HP-Prime_UG">{{cite book | title=HP Prime Graphing Calculator User Guide (UG) | publisher=Hewlett-Packard Development Company, L.P. | edition=1 | date=October 2014 | id=HP 788996-001 | url=http://h10032.www1.hp.com/ctg/Manual/c04119981.pdf | access-date=2015-10-13 | url-status=dead | archive-url=https://web.archive.org/web/20140903201341/http://h10032.www1.hp.com/ctg/Manual/c04119981.pdf | archive-date=2014-09-03 }}</ref>

* 1 decametre = 10 metres * 1 decalitre = 10 litres * 1 decare = 10 ares

Examples: * The blue whale is approximately 30 metres, or 3 decametres, in length.<ref>{{Cite web|url=http://channel.nationalgeographic.com/channel/content/kingdom-of-the-blue-whale-3302/blue-whale-facts/#/compare/length|archive-url=https://web.archive.org/web/20090306112952/http://channel.nationalgeographic.com/channel/content/kingdom-of-the-blue-whale-3302/blue-whale-facts/#/compare/length|url-status=dead|archive-date=March 6, 2009|title = National Geographic TV Shows, Specials & Documentaries}}</ref>

==As an English prefix== The prefix is used in many words.

===General=== * Decathlon, a combined event in athletics consisting of ten track and field events. * Decennial, ten-yearly or a celebration of ten years.

===Mathematics=== * Decimal based on the number ten. * Decagon a plane figure with ten sides * Decahedron a polyhedron with ten faces

===Chemistry=== * Decane, a hydrocarbon with 10 carbon atoms

===Biology=== * Decapoda, an order of crustaceans with ten feet

===Religion=== * The Decalogue, the ''Ten Commandments''

==See also== *Metric prefix

==Notes== {{notelist}}

==References== {{reflist}}

== External links == {{Wiktionary|deca-}} * [http://www.bipm.org BIPM website]

{{SI prefixes (infobox)}}

<!--Categories--> Category:SI prefixes