legitimately

from WordNet (r) 3.0 (2006)

legitimately
    adv 1: in a manner acceptable to common custom; "you cannot do
           this legitimately!" [syn: {legitimately}, {lawfully},
           {licitly}] [ant: {illegally}, {illegitimately},
           {illicitly}, {lawlessly}]
    2: in a lawfully recognized manner; "let's get married so our
       child can be born legitimately" [ant: {illegitimately}, {out
       of wedlock}]

from The Collaborative International Dictionary of English v.0.48

Legitimately \Le*git"i*mate*ly\ (-m[asl]t*l[y^]), adv.
   In a legitimate manner; lawfully; genuinely.
   [1913 Webster]