Belonging to, suitable to, or becoming, a king; characteristic of, resembling, a king; directed or administered by a king; monarchical; royal; sovereign; regal; august; noble; grand. Kingly magnificence. . A kingly government. . The kingly couch. The kingliest kings are crowned with thorn. (g. Massey) Leave kingly backs to cope with kingly cares. (Cowper)
kingly, Regal. Kingly is Anglo-Saxon, and refers especially to the character of a king; regal is latin, and now relates more to his office. The former is chiefly used of dispositions, feelings, and purposes which are kinglike; as, kingly sentiments; kingly condescension; a kingly heart for enterprises. . The latter is oftener applied to external state, pomp, etc.; as, regal state, regal title, etc. This distinction is not observed by our early writers, but is gaining ground.
Origin: Kinglier; Kingliest.
Although this citation, one from paradise lost, and one from Shakespeare's ll4th Sonnet are given by lexicographers as examples of adverbial use, it is by no means clear that the word is not an adjective in each instance.