0 a group of similar things that are close together -- grappolo, ciuffo
a cluster of galaxies un gruppo di galassie
1 to form a close group -- raggruppare, raggrupparsi, raccogliersi
2 a closely-packed group (of people or things) -- gruppo; grappolo
They stood in a cluster.
a cluster of berries
3 (often with round) to group together in clusters -- raggrupparsi
They clustered round the door.