The Collaborative International Dictionary of English v.0.48:

Twiggy \Twig"gy\, a.
   Of or pertaining to a twig or twigs; like a twig or twigs;
   full of twigs; abounding with shoots. " Twiggy trees."
   --Evelyn.
   [1913 Webster]

WordNet (r) 3.0 (2006):

twiggy
    adj 1: thin as a twig [syn: twiggy, twiglike]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "twiggy":
   attenuate, barebones, bean pole, beanstalk, bony, bowery, branched,
   branching, branchy, broomstick, clothes pole, corpse, flat,
   flat-chested, fleshless, foliaged, foliate, foliated, foliose,
   gangling, gangly, gaunt, gawky, lank, lanky, leafy, lean,
   lean-fleshed, lean-looking, leaved, leavy, meager, ramate,
   ramified, ramose, ramous, rattlebones, rawboned, reedy, scraggy,
   scrawny, shadow, skeletal, skeleton, skinny, slender, slight, slim,
   spare, spidery, spindlelegs, spindleshanks, spindling, spindly,
   stack of bones, stilt, tenuous, thin-bellied, thin-fleshed,
   undersized, underweight, walking skeleton