Source : Webster's Revised Unabridged Dictionary (1913)

Rightful \Right"ful\, a.
   1. Righteous; upright; just; good; -- said of persons. [Obs.]
      --Chaucer.

   2. Consonant to justice; just; as, a rightful cause.

   3. Having the right or just claim according to established
      laws; being or holding by right; as, the rightful heir to
      a throne or an estate; a rightful king.

   4. Belonging, held, or possessed by right, or by just claim;
      as, a rightful inheritance; rightful authority.

   Syn: Just; lawful; true; honest; equitable; proper.

Source : WordNet®

rightful
     adj 1: legally valid; "a rightful inheritance" [syn: {rightful(a)}]
     2: having a legally established claim; "the legitimate heir";
        "the true and lawful king" [syn: {true(a)}, {lawful}, {rightful(a)}]