Antonyms for the word "over-abundance" include scarcity, dearth, lack, deficiency, and insufficiency. The opposite of having too much of something is, of course, not having enough of it, and these are the precise terms that describe the opposite of "over-abundance." For example, instead of an over-abundance of food, we might speak of a scarcity of food. Instead of an over-abundance of rain, we might speak of a drought. Instead of an over-abundance of opportunities, we might speak of a lack of opportunities. By using these antonyms, we can convey the idea of scarcity or deprivation in a way that perfectly contrasts with the idea of too much or excess.