From C to C (6)
I believe the answer is:
octave
'from c to c' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for octave that I've seen before include "between two pitches" , "Span of eight notes" , "Avocet (anag.)" , "Interval involving a doubling of frequency" , "A group of eight consecutive musical notes" .)