  A novel type of symmetry breaking is reported for the two-channel Kondo
lattice where conduction electrons have spin and orbital (channel) degrees of
freedom. Using the continuous-time quantum Monte Carlo and the dynamical
mean-field theory, a spontaneous breaking of the orbital symmetry is observed.
The tiny breakdown of orbital occupation number, however, vanishes if the
conduction electrons have the particle-hole symmetry. The proper order
parameter instead is identified as a composite quantity representing the
orbital-selective Kondo effect. The single-particle spectrum of the selected
orbital shows insulating property, while the other orbital behaves as Fermi
liquid. This composite order is the first example of odd-frequency order other
than off-diagonal order (superconductivity), and is a candidate of hidden order
in $f$-electron systems.
