Overtone
An overtone is a partial, a sine wave component of a periodic sound, other than the fundamental. When no timbre is specified, it is generally assumed to be harmonic, with the result that (since the fundamental is not an overtone) the nth harmonic is the (n-1)th overtone. This is not ideal, because the interval between the mth and nth harmonic is easy to derive (n/m), whereas the interval between the mth and nth overtone is (n+1)/(m+1).
