A small, usually wooden cap enclosing the reed of certain instruments (especially early double-reed instruments) so that the player does not control it directly with his or her lips.
Origin
1960s.
Definition of reed-cap in US English:
reed-cap
noun
Music
A small, usually wooden cap enclosing the reed of certain instruments (especially early double-reed instruments) so that the player does not control it directly with his or her lips.