Which word describes a weakening mentally or morally?

The word "enervate" is indeed the appropriate choice to describe a weakening, particularly in a mental or moral context. It originates from the Latin "enervare," which means to deprive of strength or vigor. When a person or an entity is enervated, they experience a loss of energy, vitality, or moral fortitude, which fits the specification of a weakening effect.

The other words do not convey the same sense of deterioration. "Empower" implies giving someone the power or strength to do something, which is the opposite of weakening. "Enhance" suggests an improvement or increase in quality or value, while "strengthen" clearly indicates making something stronger or more robust. Thus, "enervate" stands out as it specifically addresses the aspect of reducing strength or moral capacity.