Deleteriousness is a noun that refers to the harmful or damaging effects of something. The antonyms of deleteriousness are words that describe positive, beneficial or helpful aspects. For example, beneficialness, helpfulness, advantage, healthiness, and advantageousness. Beneficialness means being advantageous and beneficial to something or someone. Helpfulness refers to the quality of being helpful or giving aid. Advantage means a condition or circumstance favorable to achieving a goal. Healthiness refers to the state of being in good health or well-being. Finally, advantageousness means being beneficial or having advantages over something. The opposite of deleteriousness are words that connote positive and uplifting meanings.