Denoting a task that can never be completed.
Late 16th century: from Latin Sisypheius (based on Greek Sisuphos: see Sisyphus)+ -an.
“It was a sisyphean task but she stuck at it.”
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.