: any of numerous small often brightly colored South American characin fishes often bred in tropical aquariums
variants
or tetr-
1
: four : having four : having four parts
tetravalent
2
: containing four atoms or groups (of a specified kind)
tetrachloride
Examples of tetra in a Sentence
Recent Examples on the Web
ArsTechnica, 25 Aug. 2025
Maine Daniel Grill/tetra Images | Tetra Images | Getty Images
No state is safer than The Pine Tree State.
—Scott Cohn, CNBC, 14 July 2025
What to Look for in the Best Chlorine Shampoos
When searching for the best chlorine shampoos, look for ingredients like apple cider vinegar, ethylene diamine tetra acetic-acid (EDTA), sodium thiosulfate, charcoal, and crystallized vitamin C to effectively remove chlorine.
—Joseph Cheatham, Men's Health, 17 July 2023
Because cavefish have evolved to live in an oxygen deficient environment, researchers weren't surprised to find that embryonic specimen exhibited more gene markers for hypoxia in comparison to the Mexican tetra.
—Daisy Hernandez, Popular Mechanics, 11 June 2020
Mexican blind cavefish, or Astyanax fasciatus, are a kind of small tetra sometimes found in home aquariums.
—Elizabeth Preston, Discover Magazine, 1 Apr. 2014
Examples are automatically compiled from online sources to
show current usage.
Read More
Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
Send us feedback.
Noun
No waste On a more fundamental level, researchers still hope to figure out why the Mexican tetra evolved into cave forms while any number of other Mexican river fish that also regularly end up in caves did not.
—ArsTechnica, 25 Aug. 2025
Maine Daniel Grill/tetra Images | Tetra Images | Getty Images
No state is safer than The Pine Tree State.
—Scott Cohn, CNBC, 14 July 2025
What to Look for in the Best Chlorine Shampoos
When searching for the best chlorine shampoos, look for ingredients like apple cider vinegar, ethylene diamine tetra acetic-acid (EDTA), sodium thiosulfate, charcoal, and crystallized vitamin C to effectively remove chlorine.
—Joseph Cheatham, Men's Health, 17 July 2023
Because cavefish have evolved to live in an oxygen deficient environment, researchers weren't surprised to find that embryonic specimen exhibited more gene markers for hypoxia in comparison to the Mexican tetra.
—Daisy Hernandez, Popular Mechanics, 11 June 2020
Mexican blind cavefish, or Astyanax fasciatus, are a kind of small tetra sometimes found in home aquariums.
—Elizabeth Preston, Discover Magazine, 1 Apr. 2014
Cite this Entry
“Tetra.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/tetra. Accessed 31 Oct. 2025.
Copy CitationKids Definition
tetra
1 of 2 noun
tet·ra
ˈte-trə 
: any of various small brightly colored South American fishes often kept in tropical aquariums
tetra-
2 of 2 combining form
: four : having four : having four parts
Etymology
Combining form
derived from Greek tetra- "four"
Love words? Need even more definitions?
Merriam-Webster unabridged
Share