The term "over-lay" refers to the act of covering or placing something on top of another thing. The opposite of over-lay is to uncover or remove something from the top. The antonym of "over-lay" is "underlay". Underlay means to place something underneath or below another thing. This word is commonly used in the construction industry, where the foundation is often laid under the building to provide a stable base. Another antonym for over-lay is "reveal", which means to disclose or uncover something that was previously hidden. In the context of art or design, "expose" can also be an antonym for over-lay, indicating the process of revealing a hidden layer beneath the surface.