Many words in the English language that seem remarkably common have a surprising secondary definition known mostly to scientists in different disciplines. Here are 18 words drawn from the American Heritage Science Dictionary that have an alternative meaning in various science disciplines. Some may be familiar, and others less so. 

1. ALIEN 

Used in: Ecology

This refers not only the drooling nightmare that terrified Sigourney Weaver but also to non-native creatures and plant species introduced to an area from which they don’t originate. 

2. ALUM

Used in: Chemistry 

When you’ve graduated from an institution of learning, you become an alumni or “alum,” but the word is also the name of any various crystalline double salts of a trivalent metal (such as aluminum, chromium, or iron) or a monovalent metal (such as potassium or sodium). It’s used in industry to harden and purify, and in medicine as an emetic (aka vomit inducer), and to stop bleeding.

3. BELT

Used in: Geography, Astronomy

You may keep your pants up with one of these, but geographers and geologists are more likely thinking of a geographic region that is in some way distinctive from others. Space scientists use this one too (see: Kuiper asteroid belt). 

4. CALCULUS 

Used in: Medicine

You may have struggled with this branch of mathematics in school, but a doctor will be more concerned with the kind that is a solid mass, usually inorganic material, that forms in a cavity or tissue of the body. Such a calculus is often found in the gall bladder, kidney or urinary bladder—otherwise known as a stone.

5. DEPOSITION

Used in: Geology

If you’re involved in a lawsuit, you may have to submit to a deposition, where a legal team asks you questions before you go to trial. For geologists, however, this refers to an accumulation of matter by natural processes, such as sediment in a river or mineral deposits in a bodily organ.

6. FAMILY 

Used in: Biology

You probably grew up in a human one and may be raising one of your own. Taxonomists use the term to mean a group of organisms ranking above a genus and below an order. Family names of plants, fungi, and algae have the suffix -aceae, while animal family names end with -idae. 

7. GALL 

Used in: Botany

It takes a lot of gall to assume there’s only one meaning to this word, which is actually an abnormal swelling of plant tissue, usually caused by injury or parasite infection. They can appear as balls, knobs, lumps, or warts. 

8. INSULT 

Used in: Medicine

A verbal attack can feel like an insult, but this term is also used for certain assaults and injuries to the body, from a bruise to a tumor. It can be the cause of such an injury as well. 

9. LISP 

Used in: Programming

Though commonly used to refer to a speech impediment, this is also an acronym for list processing, a programming language for artificial intelligence programming designed in 1959 by John McCarthy. It’s also one of the oldest programming languages still in use today.

10. MOLE

Used in: Chemistry

You may know this as an annoying little creature that digs holes in your garden (or a spy within an organization), but to chemists it’s a standard scientific unit for measuring large quantities of tiny molecules or particles. 

11. NO 

Used in: Chemistry

The word of choice for negating something is also the abbreviation for the element Nobelium, a synthetic radioactive metallic element produced by bombarding curium with carbon ions. Named after Alfred Nobel, it's radioactive. 

12. OHM 

Used in: Physics

Not to be confused with the Sanskrit word often exercised in yoga classes, an ohm is equal to the resistance of a conductor channeling one ampere of flow when a volt is applied to it.

13. PATCH

Used in: Engineering, Programming 

A torn pair of jeans might require one of these, but it’s also a temporary, removable electronic connection between two components in a communications system, as well as a piece of code that fixes a software bug.

14. RAD

Used in: Physics 

This was the equivalent of “cool” (derived from “radical”) in the 1980s, but to physicists, it’s a unit of measuring the energy absorbed by a material that has been exposed to radiation. One rad equals 100 ergs per gram of material.

15. SHEAR 

Used in: Physics

Though you can apply this to sheep to remove them of their wool, it also refers to a force applied to an object at a perpendicular angle, putting greater stress on one side of the axis than the other, as can happen in earthquakes and explosions. 

16. TAG

Used in: Programming 

Other than the game where one of you is “it” and chases down the others, this is also a term referring to a sequence of characters in a markup language to provide information for formatting specifications about a document. If you use a Mac, you might be familiar with these kinds of tags. 

17. UNION

Used in: Mathematics 

You might have to pay dues to one of these at work, but it’s also a numerical set whose members belong to at least one of a group of two or more sets. You've likely seen a union in a Venn diagram. 

18. VITRIOL

Used in: Chemistry 

It might make sense that this word, often used to mean cruel or bitter criticism, is how sulfuric acid used to be known. Discovered in the 8th century by an Arab alchemist, vitriol comes from the Latin for "glass," after its sulfate salts.