multivalence; polyvalence
Chemistry term referring to an atom or group having multiple valences or combining capacities.
Multivalent elements can exhibit multiple bonding patterns.
原子価 means 'valence' or 'atomic value'; 多原子価 specifically means 'multivalence' or 'polyvalence', i.e., having multiple valences.
Compound of 多 (た, 'many') + 原子価 (げんしか, 'valence'). A straightforward technical term in chemistry.