Step 1: "Acrimony" refers to bitterness or sharpness, especially in speech or temper. It describes a feeling of hostility or resentment that can be expressed through sharp language.
Step 2: "Apathy" refers to a lack of interest or emotion, which is not related to bitterness or sharpness.
Step 3: "Alacrity" refers to eagerness or readiness, which is also not relevant to bitterness.
Step 4: "Assiduity" refers to diligence or constant effort, which is unrelated to bitterness or sharpness.
Thus, the correct answer is "Acrimony."