Etymology Dictionary

RANKLE,  to fester.  (E.)   In Levins; spelt rankyll in Palsgrave.   Lit. to grow rank; but, being derived from rank only in the M.E. period, it took up the later sense of rank, after it had been confused with F. rance or ranci, 'musty, fusty, stale, putrified,' Cot.; as noticed under Rank (2).   It is rare in M.E., but appears, according to Stratmann, in Sir Beves of Hamptoun, ed. Turnbull, l. 2656.   Formed from Rank (2) by the addition of the frequentative suffix -le.   Hence the sense is 'to keep on being rank,' to fester continually.   But see Addenda. [※]

ADDENDA

Perhaps (F.,—L.) rather than (E.).   We find the sb. rancle, a festering sore, in the 14th cent.; see Reliq. Antiquæ, i. 52, 53.   Also rancle, verb, as in:  'maake the legges to rancle;' Book of St. Albans, fol. a 3, back.   The sb. corresponds to Anglo-F. rancle, a sore, in the Life of Edw. Conf. 2677; we also find the pp. f. ranclee, festered, and the pp. arancle, putrified, in the same ll. 4166, 2615.   These are forms of the 12th century.   These words are to be connected with F. rance, putrified, rather than with E. rank, coarse in growth; and F. rance is from Lat. acc. rancidum; see Rancid.   The confusion between E. rank and F. rance has already been pointed out; see Rank (2).