The Collaborative International Dictionary of English v.0.48:

Seedling \Seed"ling\, n. (Bot.)
   A plant reared from the seed, as distinguished from one
   propagated by layers, buds, or the like.
   [1913 Webster] Seedlip

WordNet (r) 3.0 (2006):

seedling
    n 1: young plant or tree grown from a seed

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "seedling":
   amphibian, angiosperm, annual, aquatic plant, biennial, conifer,
   cosmopolite, cutting, deciduous plant, dicot, dicotyledon,
   ephemeral, evergreen, exotic, flowering plant, fruit tree, fungus,
   gametophyte, gymnosperm, hardwood tree, hydrophyte, monocot,
   monocotyl, perennial, plant, pollard, polycot, polycotyl,
   polycotyledon, sapling, scion, seed plant, set, shade tree, shoot,
   slip, softwood tree, spermatophyte, sporophyte, sprig, sprout,
   sucker, thallophyte, timber, timber tree, tree, triennial, twig,
   vascular plant, vegetable, weed