The Collaborative International Dictionary of English v.0.48:

Offshoot \Off"shoot`\, n. [Off + shoot.]
   That which shoots off or separates from a main stem, channel,
   family, race, etc.; as, the offshoots of a tree.
   [1913 Webster]

WordNet (r) 3.0 (2006):

offshoot
    n 1: a natural consequence of development [syn: outgrowth,
         branch, offshoot, offset]

Moby Thesaurus II by Grady Ward, 1.0:

175 Moby Thesaurus words for "offshoot":
   V, accession, accessory, accompaniment, addenda, addendum,
   additament, addition, additive, additory, additum, adjunct,
   adjuvant, affiliate, affiliation, annex, annexation, appanage,
   appendage, appendant, appurtenance, appurtenant, arm, attachment,
   augment, augmentation, bine, body, bough, branch, branch office,
   branchedness, branchiness, breakaway group, burgeon, by-product,
   camp, caucus, chapter, church, coda, communion, community,
   complement, concomitant, consequence, consequent, continuation,
   corollary, crotch, crutch, deadwood, delta, denomination,
   derivation, derivative, descendant, development, distillate,
   division, effect, ethnic group, event, eventuality, eventuation,
   extension, extrapolation, faction, fan, fellowship, filiation,
   fixture, flagellum, fork, frond, fruit, furcula, furculum, groin,
   group, hand, harvest, heir, imp, increase, increment, inguen,
   interest, interest group, issue, joint, kin, kindred, leg, legacy,
   limb, link, lobe, lobule, local, lodge, logical outcome, member,
   minority group, offset, offspring, order, organ, organization,
   outcome, outgrowth, party, pendant, persuasion, pinion,
   political party, post, precipitate, pressure group, product, prong,
   ramage, ramification, reinforcement, relation, relative,
   religious order, result, resultant, runner, sarment, schism,
   school, scion, sect, sectarism, segment, sequel, sequela, sequence,
   sequent, shoot, side, side effect, side issue, silent majority,
   slip, society, spear, spin-off, splinter, splinter group, spray,
   sprig, sprit, sprout, spur, stem, stolon, sucker, supplement,
   switch, tail, tailpiece, tendril, thallus, trident, twig,
   undergirding, upshot, variety, version, vocal minority, wing,
   wishbone