Cluster belongs to a small club of English words that survived the Norman Conquest without a scratch. Old English clyster meant a bunch or group — probably of grapes or berries originally — and simply never got displaced by a French rival. Its deeper roots are uncertain, but it appears to sit within a Proto-Germanic family of words involving things stuck or clumped together: clot, clump, clutch, and possibly clutter all seem to share the same instinct. The word held steady through Middle English and into the modern period, picking up new applications along the way. Astronomers adopted it for star clusters in the 18th century, while military usage gave us cluster bombs in the 20th. Computing borrowed it in the 1970s for groups of linked servers working as one system. Statisticians speak of cluster analysis. In every case the core image remains identical to what an Anglo-Saxon farmer saw in a bunch of grapes: similar things pressed close together. Few English words can claim such unbroken semantic continuity.