NOUN (2)

1. a series of chemical reactions in which the product of one is a reactant in the next;

2. a self-sustaining nuclear reaction; a series of nuclear fissions in which neutrons released by splitting one atom leads to the splitting of others;

WordNet (r) 3.0 (2006):

chain reaction
    n 1: a series of chemical reactions in which the product of one
         is a reactant in the next
    2: a self-sustaining nuclear reaction; a series of nuclear
       fissions in which neutrons released by splitting one atom
       leads to the splitting of others

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "chain reaction":
   Indian file, alpha decay, array, articulation, atom-chipping,
   atom-smashing, atomic disintegration, atomic reaction, atomization,
   bank, beta decay, bombardment, breeding, bullet, buzz, catena,
   catenation, chain, chain of circumstances, chaining,
   chapter of accidents, cleavage, concatenation,
   concatenation of events, connection, consecution, continuum,
   course, cycle, descent, disintegration series, dissociation, drone,
   endless belt, endless round, exchange reaction, feast and famine,
   file, filiation, fission, fission reaction, gamma decay, gamut,
   gradation, hum, ins and outs, ionization, line, lineage, monotone,
   neutron reaction, nexus, nonreversible reaction, nuclear fission,
   nucleization, pendulum, periodicity, photodisintegration, plenum,
   powder train, progression, proton gun, proton reaction, queue,
   range, rank, recurrence, reticulation, reversible reaction,
   rotation, round, routine, row, run, scale, sequence, series,
   single file, spectrum, splitting the atom, stimulation, string,
   succession, swath, target, thermonuclear reaction, thread, tier,
   train, ups and downs, vicious circle, vicissitudes,
   vicissitudes of fortune, windrow