fitness

American  

[fit-nis] / ˈfɪt nɪs /

noun

1. health.

2. capability of the body of distributing inhaled oxygen to muscle tissue during increased physical effort.

3. Also called Darwinian fitness.  Biology.

   1. the genetic contribution of an individual to the next generation's gene pool relative to the average for the population, usually measured by the number of offspring or close kin that survive to reproductive age.

   2. the ability of a population to maintain or increase its numbers in succeeding generations.

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fitness British  

/ ˈfɪtnɪs /

noun

1. the state of being fit

2. biology

   1. the degree of adaptation of an organism to its environment, determined by its genetic constitution

   2. the ability of an organism to produce viable offspring capable of surviving to the next generation

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Etymology

Origin of fitness

First recorded in 1570–80; fit ¹ + -ness

Explanation

Fitness is good physical condition. If you're a fitness nut and you're constantly working out, everybody else at the gym might be eyeing your sculpted muscles with envy and marveling at your stamina and strength. Fitness can also refer to your being fit, or qualified, for something. If you show up in ragged jeans and a dirty t-shirt to interview for a job in the clean room of a microchip factory, your interviewer might question your fitness for the position. For a ship, fitness is a measure of whether it's seaworthy. In biology, an organism's fitness for a particular environment is its ability to survive and reproduce in those conditions.

Example Sentences

They are commonly used by the fitness community and biohackers.

From MarketWatch • Apr. 15, 2026

"Rory is as fit as a fiddle. He's so diligent with his fitness work. I think virtually every day he does an hour just working on his legs," said Brown.

From BBC • Apr. 13, 2026

The 25-year-old, who lives in Manchester, follows a lot of fitness and wellness influencers - and says she gets annoyed by content from some of them "demonising" hormonal contraception and calling it "unnatural".

From BBC • Apr. 11, 2026

To maintain that sense of community after ending the classes, she reallocated some of her budget to fitness and got a ClassPass membership for $19 monthly.

From The Wall Street Journal • Apr. 10, 2026

Age had thickened her husband, thinned his hair, and reduced the numerology by which Bull himself measured his fitness.

From "The Great Santini" by Pat Conroy

Related Words

• adequacy
• compatibility
• competence
• consistency
• eligibility
• preparedness
• qualification
• readiness
• suitability