tetra-
Prefix meaning 'four', used in scientific and technical terms such as テトラポッド (tetrapod) or テトラコード (tetrachord).
Tetrapods are used to prevent coastal erosion.
tetra (fish)
Refers to small tropical freshwater fish of the family Characidae, popular in aquariums.
I keep ten neon tetras in the aquarium.
rainbow tetra
diamond tetra
tetrachloroethylene
From English 'tetra-', ultimately from Ancient Greek 'tetra-' meaning 'four'. The fish sense is a clipping of 'Tetragonopterus', an old genus name.