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The discovery of a charge-density wave (CDW) in a-U at ~43 K is reported. The mode corresponds to the condensation of a longitudinal-optic phonon near q = [ 2,0,0] in which the atoms are displaced by ~0.006 A from their special positions. Large precursor effects are seen in the phonon spectra. The wave vector of the CDW is related to that of the fundamental lattice in a rather complex way, which is discussed in terms of discommensurations between the CDW (OL' phase) and the primary a phase.