Main Entry: ¹clus·ter

Pronunciation: \ˈkləs-tər\

Function: noun

Etymology: Middle English, from Old English clyster; akin to Old English clott clot

Date: before 12th century

: a number of similar things that occur together: as a : two or more consecutive consonants or vowels in a segment of speech b : a group of buildings and especially houses built close together on a sizable tract in order to preserve open spaces larger than the individual yard for common recreation c : an aggregation of stars or galaxies that appear close together in the sky and are gravitationally associated d : a larger than expected number of cases of disease (as leukemia) occurring in a particular locality, group of people, or period of time

— clus·tery \-t(ə-)rē\ adjective