a. (sb.) Math. [f. BI- pref.2 II + ORDINAL, f. L. ordo, ordin-, rank, order.]
A. adj. Of the second order.
1853. De Morgan, Camb. Philos. Trans., IX. IV. 2. It is desirable to invent single words to stand for the phrases ‘of the first order,’ ‘of the second order,’ etc. I propose primordinal, biordinal, etc. The word differential may be dispensed with, since these adjectives are understood to apply to differential equations only.
B. sb. A linear differential equation of the second order: see ORDINAL.
1881. Sir J. Cockle, in Athenæum, 268. [Paper entitled] ‘Supplement on Binomial Biordinals.’
