The Compact Edition of the Oxford English Dictionary (1971) defines Castor
as "1.The beaver (now rarely used). . . . 2. A reddish-brown unctuous
substance having a strong smell and nauseous bitter taste, obtained from
two sacs in the inguinal region of the beaver; used in medicine and
perfumery; castoreum. . . .3. A hat, orig, either of beaver's fur, or
intended to be taken as such; in the end of the 17th and beginning of the
18th c. distinguished from beaver' and said to be of rabbit's fur; at that
time also usually spelt caster . . . ."
Paul Schrank
Raleigh, NC