Clef and Viola clef

Clef noun - A musical notation written on a staff indicating the pitch of the notes following it.

Viola clef and clef are semantically related. In some cases you can replace phrase "Viola clef" with "Clef", this terms are similar.

Viola clef noun - A clef that puts middle C on the third line of a staff.

Clef and viola clef are semantically related. You can use "Clef" instead a noun phrase "Viola clef".