A condition in which there is only one finger or toe on each hand or foot.
Late 19th century: from monodactyl (from Greek monodaktulos ‘one-fingered’) + -y.
“Though horses are mondactyl creatures, researchers think they once had many toes.”
With regard to, or at the level of, orders in a taxonomic system; according to an ordinal number, system, etc.; on an ordinal scale; with regard to order.
Mid 19th century; earliest use found in The Edinburgh Review. From ordinal + -ly.