The word "clog up" refers to a situation where something becomes blocked, obstructed or stops functioning properly due to an excess of material. Antonyms for this term could be "unclog," "clear," "open," "flow," or "drain." To unclog something means to remove any blockages or obstructions that are preventing it from functioning as intended. Clearing out a clogged drain or pipe can relieve the pressure and allow fluids to move through freely. Opening up a previously blocked pathway or channel can lead to an improved flow of traffic. The opposite of clog up can also be expressed by using the term "free," which means to remove any constraints or barriers to movement.