1. a musical notation written on a staff indicating the pitch of the notes following it;
The Collaborative International Dictionary of English v.0.48:
Clef \Clef\ (kl[e^]f; 277), n. [F. clef key, a key in music, fr.
L. clavis key. See Clavicle.] (Mus.)
A character used in musical notation to determine the
position and pitch of the scale as represented on the staff.
Note: The clefs are three in number, called the C, F, and G
clefs, and are probably corruptions or modifications of
these letters. They indicate that the letters of
absolute pitch belonging to the lines upon which they
are placed, are respectively C, F, and G. The F or bass
clef, and the G or treble clef, are fixed in their
positions upon the staff. The C clef may have three
positions. It may be placed upon the first or lower
line of the staff, in which case it is called soprano
clef, upon the third line, in which case it called alto
clef, or upon the fourth line, in which case tenor
clef. It rarely or never is placed upon the second
line, except in ancient music. See other forms of C
clef under C, 2.
Alto clef, Bass clef. See under Alto, Bass.
WordNet (r) 3.0 (2006):
n 1: a musical notation written on a staff indicating the pitch
of the notes following it