The Collaborative International Dictionary of English v.0.48:

Runty \Runt"y\, a.
   Like a runt; diminutive; mean.
   [1913 Webster]

WordNet (r) 3.0 (2006):

runty
    adj 1: well below average height [syn: pint-size, pint-
           sized, runty, sawed-off, sawn-off]
    2: (used especially of persons) of inferior size [syn: puny,
       runty, shrimpy]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "runty":
   Lilliputian, Tom Thumb, couchant, crouched, debased, depressed,
   dumpy, dwarf, dwarfed, dwarfish, elfin, flat, incipient, knee-high,
   knocked flat, laid low, low, low-built, low-hung, low-level,
   low-leveled, low-lying, low-set, low-statured, meager, midget,
   nanoid, neap, prone, pygmy, recumbent, rudimental, rudimentary,
   scraggy, scrubby, short, shriveled, shrunk, shrunken, squat,
   squatty, stooped, stumpy, stunt, stunted, supine, undersize,
   undersized, unelevated, wizened