The antonyms for the word "making null and void" would be words or phrases that mean the opposite of cancelling or voiding something. Some possible antonyms may include validating, confirming, affirming, legitimizing, endorsing, or authorizing. These terms would suggest that something has been deemed valid or legally binding, rather than being cancelled or rendered void. Additionally, terms such as enforcing, executing, implementing, or carrying out may also serve as antonyms, as they imply the completion or enforcement of an action rather than its cancellation. Ultimately, the choice of antonym depends on the specific context in which the phrase "making null and void" is being used.