Definition of biordinal in English:
biordinal
adjective bʌɪˈɔːdɪnlbʌɪˈɔːd(ə)nl
Entomology. Of hooks on the prolegs of caterpillars: arranged in a straight line or circle, and of two different, alternating, lengths.
Origin
Mid 19th century (in an earlier sense). From bi- + ordinal.