1.  aggregation(n = noun.group) accumulation, assemblage, collection - several things grouped together or considered as a whole;

2.  aggregation(n = noun.act) assembling, collecting, collection - the act of gathering something together;

   The act of aggregating, or the state of being aggregated; collection into a mass or sum; a collection of particulars; an aggregate. [1913 Webster]

N  coherence, adherence, adhesion, adhesiveness, concretion accretion, conglutination, agglutination, agglomeration, aggregation, consolidation, set, cementation, sticking, soldering, connection, dependence, tenacity, toughness, stickiness, inseparability, inseparableness, bur, remora, conglomerate, concrete, cohesive, adhesive, adhering, cohering, tenacious, tough, sticky, united, unseparated, unsessile, inseparable, inextricable, infrangible, compact.

N  assemblage, collection, collocation, colligation, compilation, levy, gathering, ingathering, muster, attroupement, team, concourse, conflux, congregation, contesseration, convergence, meeting, levee, reunion, drawing room, at home, conversazione, assembly, congress, convention, conventicle, gemote, conclave, posse, posse comitatus, Noah's ark, miscellany, collectanea, museum, menagerie, museology, crowd, throng, group, flood, rush, deluge, rabble, mob, press, crush, cohue, horde, body, tribe, crew, gang, knot, squad, band, party, swarm, shoal, school, covey, flock, herd, drove, atajo, bunch, drive, force, mulada, remuda, roundup, array, bevy, galaxy, corps, company, troop, troupe, task force, army, regiment, host, populousness, clan, brotherhood, fraternity, sorority, association, volley, shower, storm, cloud, group, cluster, Pleiades, clump, pencil, set, batch, lot, pack, budget, assortment, bunch, parcel, packet, package, bundle, fascine, fasces, bale, seron, seroon, fagot, wisp, truss, tuft, shock, rick, fardel, stack, sheaf, haycock, fascicle, fascicule, fasciculus, gavel, hattock, stook, accumulation, congeries, heap, lump, pile, rouleau, tissue, mass, pyramid, bing, drift, snowball, snowdrift, acervation, cumulation, glomeration, agglomeration, conglobation, conglomeration, conglomerate, coacervate, coacervation, coagmentation, aggregation, concentration, congestion, omnium gaterum, spicilegium, black hole of Calcutta, quantity, collector, gatherer, whip, whipper in, assembled, closely packed, dense, serried, crowded to suffocation, teeming, swarming, populous, as thick as hops, all of a heap, fasciculated cumulative, the plot thickens, acervatim, tibi seris tibi metis.