Dihydrogen Monoxide (or DHMO) is a tongue in cheek conspiracy theory that claims said substance is extremely dangerous, can cause burns, death, etc., when in reality, dihydrogen monoxide is the scientific name for water, as H2O is its chemical formula.
Person 1: Careful! There might be DHMO in your water!
Person 2: Dihydrogen Monoxide IS water.
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In today's lab, you're gonna be working with dihydrogen monoxide. Now in large amounts, it could cause suffocation and death. If the subtance is heated, it could cause severe burns. Cold versions of this substance can also cause frostbite. Handle this lab with extreme caution, please.
by Ichigo69 November 01, 2009
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Sometimes shortened to DHMO or {H2O, it is the molecular name for water. For more information about chemistry, go to a science website. For more information about water, visit your local water bottle

NOTE: Being such a rare term, it is commonly used by 4Chan to prank people. A common prank is listed below.
Did you know that there is a substance called Dihydrogen Monoxide that causes a lot of death and disturbance every second? When you breathe DHMO, you die. But Big Pharma doesn't want you to know! Dihydrogen Monoxide is present in every single vaccine, and 100% of Autistic children have drunk it. Big Pharma has put DHMO in all your medicines, and even Homeopathy cannot exist without it. If you drink too much, you die. But yet, you are given DHMO at the doctor's office when you ask for water. SMH my head Big Pharma will never learn
by swntimentoffreedom May 21, 2019
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