subs. phr. (old).A physician: a velvet-cap formed a distinctive part of a doctors garb.
1606. The Return from Parnassus, ii., 1 [DODSLEY, Old Plays, 1874, ix. 132]. Theodore. O Monsier, I have a singular care of your valetudo. It is requisite that the French physicians be learned and careful; your English VELVET-CAP is malignant and envious.