Tet·ra-
  1. A combining form or prefix signifying four, as in tetrabasic, tetrapetalous.
  2. Chem. A combining form (also used adjectively) denoting four proportional or combining parts of the substance or ingredient denoted by the term to which it is prefixed, as in tetra-chloride, tetroxide.
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  tetra
       n : brightly colored tropical freshwater fishes