The word "making heavy" can have several antonyms, depending on the context in which it is used. One opposite of 'making heavy' could be 'lightening,' which means to make something less heavy. Another antonym could be 'easing,' which means to make something less difficult or tense. 'Lifting' could also be an antonym of 'making heavy,' as it implies that something is being raised or made lighter. Furthermore, 'unburdening,' 'relieving,' and 'freeing' could all be antonyms of 'making heavy,' as they refer to the removal or release of weight, pressure, or stress from something. Ultimately, the antonym of 'making heavy' depends on the specific context and how the word is being used.