n.
  - a group of similar things or people positioned or occurring closely together. ▸a natural subgroup of a population, used for statistical sampling or analysis. 
- Chemistry  a group of atoms of the same element, typically a metal, bonded closely together in a molecule.
v.
 form a cluster. 
▸Statistics  (of data points) have similar numerical values.
Derivative
  
  Etymology
  OE clyster; prob. rel. to clot.