  Bianisotropy of metaatoms is usually associated with their nonlocal response
and the mutual coupling between electric and magnetic dipole moments induced by
the incident field. In this work, we generalize the theory of bianisotropy
beyond the dipole response to the cases of arbitrary high-order multipole
resonances. We demonstrate that bianisotropy is exclusively caused by the
absence of the inversion symmetry of metaatoms. The strength of the
bianisotropy response is normally increased with the size of a meta-atom but
its origin is fully connected to the symmetry of the structure. As an important
example of bianisotropic particle, we consider a triangular prism and show how
accounting for the higher-order multipoles prevents the violation of the
Onsager-Casimir conditions for kinetic coefficients appearing in the dipole
approximation. The developed theory is an important step towards a deeper
insight into the scattering properties of nanoantennas and meta-atoms.
