This name may be derived from the Danish Rank, right, upright, erect. If the name is Gaelic, it would come from Roinn, a promontory, share, or division, and Ceann, head; the head of the promontory, a name of place. Ranken, in the Dutch, signifies pranks, tricks.

Arthur, William (1857) An Etymological Dictionary of Family and Christian Names. New York: Sheldon, Blakeman. Public Domain.

RANKIN. I always considered this a diminutive of Randolf (see Hankin) ; but there is a tradition of descent from one John, son of a knight called Jacob de Rankine, burgomaster of Ghent, who married a daughter of the head of the house of Keith, and became progenitor of the Rankines, Ranking, Rankens, Rankings, and Rangkings of Scotland, who are i-ather numerous in the West, and on the border. The tradition is, however, dateless and vague. Inf. M. H. Rankin, Esq.

Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.