• (n.) A feather which has a plumelike web, with the shaft of an ordinary feather.
Sem'i·plume` (sĕm`ĭ*plūm) noun (Zoology) A feather which has a plumelike web, with the shaft of an ordinary feather. 
semiplume 1. A feather intermediate in type between a contour feather (body feather, as opposed to a wing or tail feather) and down. 2. A feather which has a plume-like web, with the shaft of an ordinary feather.