Entry 2 senses Webster, 1913

Involucrum

· In·vo·lu·crum · IPA /ˌɪnvəˈluːkɹəm/

01 n. See Involucre.

pl. Involucra, Involucrums ((#))

1.
See Involucre.(Bot.) See: Involucre
2.
A sheath which surrounds the base of the lasso cells in the Siphonophora.(Zool.)