\In*vol"u*cel\ (?; 277), n. [Dim. of involucre, or
involucrum: cf. F. involucelle.] (Bot.)
A partial, secondary, or small involucre. See Illust. of
{Involucre}.
Biology Dictionary
Definition:
A secondary involucre, as the bracts subtending the secondary umbels in the family Umbelliferae.
Webster's 1913 Dictionary