Which of the following words means insufficient?

The word "scant" specifically refers to something that is inadequate or insufficient in quantity, size, or degree. It conveys a sense of something being barely enough or falling short of what is necessary. This definition aligns perfectly with the question regarding a word that means insufficient, making "scant" the appropriate choice.

The other words do not carry the same meaning. "Onerous" describes something burdensome or involving a lot of effort, "tawdry" refers to something that is showy but of poor quality, and "unequivocal" means clear and unambiguous. None of these terms relate to the concept of insufficiency, reinforcing why "scant" is the correct response.