nadir#Medicine

Although it entered English via other European languages, the word “nadir” is ultimately an Arabic loanword. It comes from the Arabic word “nazir”, meaning “opposite to”. More specifically, it originated from the Arabic phrase “nazir as-samt”, meaning “[the] opposite direction”.”nadir (n.)”. etymonline. Web. Accessed 18 Mar 2025. https://www.etymonline.com/word/nadir

Hebrew (whether ancient or modern) is a related language to Arabic, as they are both Semitic languages.Testen, David. “Semitic languages”. Encyclopedia Brittanica. Last updated 24 Feb 2025. Web. Accessed 18 Mar 2025. https://www.britannica.com/topic/Semitic-languages Hebrew also has a word “nadir” (נדיר), but with a somewhat different meaning: it is an adjective meaning “rare”.”Inflection of נדיר. Pealim [“Verbs”]. Web. Accessed 18 Mar 2025. https://www.pealim.com/dict/3316-nadir/ However, the same word also has a specialized usage to match its meaning in other languages like English.”nadir”. Do it in Hebrew. Hebrew-English online dictionary. Web. Accessed 18 Mar 2025. https://doitinhebrew.com/Translate/default.aspx?kb=US+US&l1=en&l2=iw

File:Nadir Viewing Geometry.svg sunlight in the nadir viewing geometry.]]

Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous terms. Specifically, in astronomy, geophysics and related sciences (e.g., meteorology), the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location.

The term can also be used to represent the lowest point that a celestial object reaches along its apparent daily path around a given point of observation (i.e. the object's lower culmination). This can be used to describe the position of the Sun, but it is only technically accurate for one latitude at a time and only possible at the low latitudes. The Sun is said to be at the nadir at a location when it is at the zenith at the location's antipode and is 90° below the horizon.

Nadir also refers to the downward-facing viewing geometry of an orbiting satellite,{{cite web |url=http://spacecraft.ssl.umd.edu/design_lib/ICES01-2435.ISS_CBM.pdf |last=McLaughlin |first=Richard J. |last2=Warr |first2=William H. |title=The Common Berthing Mechanism (CBM) for International Space Station |publisher=Society of Automotive Engineers |year=2001 |access-date=March 23, 2012 |archive-url=https://web.archive.org/web/20060915203048/http://spacecraft.ssl.umd.edu/design_lib/ICES01-2435.ISS_CBM.pdf |archive-date=September 15, 2006 |url-status=dead }} such as is employed during remote sensing of the atmosphere, as well as when an astronaut faces the Earth while performing a spacewalk. A nadir image is a satellite image or aerial photo of the Earth taken vertically. A satellite ground track represents its orbit projected to nadir on to Earth's surface.

Generally in medicine, nadir is used to indicate the progression to the lowest point of a clinical symptom (e.g. fever patterns) or a laboratory count. In oncology, the term nadir is used to represent the lowest level of a blood cell count while a patient is undergoing chemotherapy.{{cite web|title=Bone marrow suppression|url=http://www.cancer.org/Treatment/TreatmentsandSideEffects/TreatmentTypes/Chemotherapy/ChemotherapyPrinciplesAnIn-depthDiscussionoftheTechniquesanditsRoleinTreatment/chemotherapy-principles-chemo-side-effects-bone-marrow-suppression|work=Chemotherapy Principles: An In-depth Discussion|publisher=American Cancer Society|access-date=March 5, 2013|archive-url=https://web.archive.org/web/20100721225530/http://www.cancer.org/Treatment/TreatmentsandSideEffects/TreatmentTypes/Chemotherapy/ChemotherapyPrinciplesAnIn-depthDiscussionoftheTechniquesanditsRoleinTreatment/chemotherapy-principles-chemo-side-effects-bone-marrow-suppression|archive-date=July 21, 2010}} A diagnosis of neutropenic nadir after chemotherapy typically lasts 7–10 days.{{Cite book |last=Le |first=Tao |url=https://books.google.com/books?id=ppEG-KuGMdoC |title=First Aid for the USMLE Step 2 CK |last2=Bhushan |first2=Vikas |last3=Skapik |first3=Julia |publisher=McGraw Hill Professional |year=2007 |isbn=978-0-07-159457-8 |edition=6. |location=London |page=479 |language=en}}{{Clear}}

The word is also used figuratively to mean a low point, such as with a person's spirits,{{cite EB1911 |wstitle=Nadir |volume=19 |page=149}} the quality of an activity or profession,{{cite news |url=http://www.timesonline.co.uk/tol/comment/columnists/janice_turner/article2980262.ece |title=The lowest point in British journalism |work=The Times |first=Janice |last=Turner |date=December 1, 2007 |archive-url=https://web.archive.org/web/20080905234436/http://www.timesonline.co.uk/tol/comment/columnists/janice_turner/article2980262.ece |archive-date=September 5, 2008 |access-date=March 23, 2012}} or the nadir of American race relations.{{Cite book |last=Logan |first=Rayford Whittingham |title=The betrayal of the Negro: from Rutherford B. Hayes to Woodrow Wilson |publisher=DaCapo Press |year=1997 |isbn=978-0-306-80758-9 |edition=1. |location=New York, NY |oclc=35777358 |orig-year=1965}}

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