The Collaborative International Dictionary of English v.0.48:

Rangy \Ran"gy\ (r[=a]n"j[y^]), a. [From Range, v. i.]
   Inclined or able to range, or rove about, for considerable
   distances; apt or suited for much roving, -- chiefly used of
   cattle.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

rangy
    adj 1: tall and thin and having long slender limbs; "a gangling
           teenager"; "a lanky kid transformed almost overnight into
           a handsome young man" [syn: gangling, gangly,
           lanky, rangy]
    2: adapted to wandering or roaming
    3: allowing ample room for ranging