[ fat ]
/ fæt /
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See synonyms for: fat / fats / fatted / fatter on Thesaurus.com

adjective, fat·ter, fat·test.
verb (used with or without object), fat·ted, fat·ting.
to make or become fat.
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Idioms about fat

Origin of fat

First recorded before 1000; Middle English; Old English fǣtt, originally the past participle of fǣtan “to cram, load, adorn”; cognate with Gothic fētjan “to adorn”; akin to vat

synonym study for fat

1. See stout.



fat , phat
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What is a basic definition of fat?

Fat is commonly used as a way to describe someone as obese or overweight.

This is most often used in a critical, judgmental, or mean way. In contrast, words like obese and overweight are more often used in a neutral way, such as in a medical context in the discussion of a person’s health (though they too can be used in a judgmental or mean way).

This sense of fat isn’t always used in a negative way. Some people might call others or themselves fat in a way that’s not intended to be critical, as in I’m fat and I’m fabulous and all the body-shamers will just have to deal with it. 

Sometimes, people replace the word fat with words intended to be more polite or euphemistic, such as heavy, heavyset, plump, and chubby. However, these words still focus on a person’s weight or appearance in a way that can be demeaning or objectifying.

As a noun, fat refers to the greasy substance that forms some types of tissue in the body of humans and animals (some of which the body stores and uses for energy) and some plants. The word is often used more casually to refer to a person’s excess flesh, as in belly fat.  

In the context of nutrition, fat refers to this kind of substance in the foods we eat. Foods from animals, such as meat, milk, and eggs, all contain fat. But so do some plant-based foods, such as nuts, avocados, and olive oil. However, there are different kinds of fat, such as saturated fat, unsaturated fat, and trans-fat, each of which can have different effects on a person’s nutrition and health. In general, it’s usually recommended not to consume too much fat. However, some fats are necessary in a diet because they help the body to absorb vitamins. The nutrition label on food products usually tell you exactly how much fat and what kinds of fats are in them.

The word fat is common and has many other meanings as an adjective, a noun, and even a verb.

Example: This diet is based on avoiding foods that are high in fat.  

Where does fat come from?

The first records of the word fat come from before the year 1000. It comes from the Old English verb fǣtan, meaning “to cram” or “to load.”

Many of the meanings of fat involve the idea of excess. As an adjective, it’s often used to describe someone who’s considered to have an excess of fatty tissue in their body—a judgment that’s simply inappropriate outside of medical advice. When used in a figurative way, the noun fat refers to something that’s excessive or unnecessary, as in We need to trim the fat from this budget and focus on the essentials.

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What are some other forms related to fat?

What are some synonyms for fat?

What are some words that share a root or word element with fat

What are some words that often get used in discussing fat?

How is fat used in real life?

Fat is an extremely common word with many different meanings. It’s offensive to call a person fat in a mean or judgmental way.


Try using fat!

True or False? 

Only foods from animals contain fat.

How to use fat in a sentence

British Dictionary definitions for fat

/ (fæt) /

adjective fatter or fattest
verb fats, fatting or fatted
to make or become fat; fatten

Derived forms of fat

Word Origin for fat

Old English fǣtt, past participle of fǣtan to cram; related to Old Norse feita, Old High German feizen to fatten; compare Gothic fētjan to adorn
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for fat

[ făt ]

Any of a large number of oily compounds that are widely found in plant and animal tissues and serve mainly as a reserve source of energy. In mammals, fat, or adipose tissue, is deposited beneath the skin and around the internal organs, where it also protects and insulates against heat loss. Fat is a necessary, efficient source of energy. An ounce of fat contains more than twice as much stored energy as does an ounce of protein or carbohydrates and is digested more slowly, resulting in the sensation of satiety after eating. It also enhances the taste, aroma, and texture of food. Fats are made chiefly of triglycerides, each molecule of which contains three fatty acids. Dietary fat supplies humans with essential fatty acids, such as linoleic acid and linolenic acid. Fat also regulates cholesterol metabolism and is a precursor of prostaglandins. See more at saturated fat unsaturated fat.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Other Idioms and Phrases with fat


The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.