Noah Webster's Dictionary (adv.) According to right or justice.

Multi-Version Concordance Rightfully (3 Occurrences) Psalms 112:5 Well is it with the man that dealeth graciously and lendeth; He shall maintain his cause in judgment. (See JPS) Isaiah 49:24 Shall the prey be taken from the mighty? and shall he that is rightfully captive be delivered? (DBY) Ezekiel 21:27 A ruin, a ruin, a ruin, will I make it; this also shall be no more, until he come whose right it is, and I will give it him. (See NIV)