coleoptile

noun

co·​le·​op·​tile ˌkō-lē-ˈäp-tᵊl 

: the first leaf of a monocotyledon forming a protective sheath about the plumule

Word History

Etymology

New Latin coleoptilum, from Greek koleon + ptilon down; akin to Greek pteron

First Known Use

circa 1866, in the meaning defined above