From The Collaborative International Dictionary of English v.0.48 :
Disproportional \Dis`pro*por"tion*al\, a.
Not having due proportion to something else; not having
proportion or symmetry of parts; unsuitable in form, quantity
or value; inadequate; unequal; as, a disproportional limb
constitutes deformity in the body; the studies of youth
should not be disproportional to their understanding.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
disproportional
adj 1: out of proportion [syn: disproportionate,
disproportional] [ant: proportionate]