The antonyms for the word "jam full" are scarce, empty, and depleted. When something is scarce, it is in short supply, and there is not enough of it to go around. Similarly, when something is empty, it means that it is void of anything and lacks substance. Depleted is another antonym of jam full, which means that something is exhausted or has reached a low point. It's essential to understand these antonyms to have a clear understanding of the opposite of jam full, which is a condition when something is fully packed, crowded, or filled to capacity. So, you can use these antonyms to contrast and describe a state of insufficiency, emptiness, or exhaustion.