Polarized Cu K x-ray absorption near-edge structure spectra of CuO are measured and analyzed with the aim of extracting quadrupole and dipole partial spectral components. Theoretical spectral components are calculated within the framework of real-space multiple-scattering technique, relying on a non-self-consistent muffintin potential. A local coordinate system x8y8z8 suitable for polarization analysis is defined by the sides of the CuO4 quasirectangle rather than by directions of the Cu-O bonds. An exclusively quadrupole nature of the prepeak is established both experimentally and theoretically. By analyzing the experimental data, we find that those states which give rise to the prepeak lie within the CuO plane, and have mainly a dx8y8 character. The theory correctly reproduces gross features of the polarized structure generated by dipole transitions, apart from a spurious peak at 8983 eV for the pz8 component. A partial agreement between theory and experiment in the shoulder region suggests that this structure may arise partly from one-electron states and partly from manybody processes.