The antonyms for the word "tip-up" include "stable," "fixed," "steady," "level," and "secure." These words describe something that is firmly in place and not easily moved or tilted. Additionally, antonyms for "tip-up" can be "downward," "sagging," or "drooping," which describe something that is lower or sinking rather than raised or erect. "Flat," "horizontal," and "even" can also be antonyms for "tip-up," indicating the absence of an upwards slope or angle. Overall, the antonyms for "tip-up" emphasize stability and immobility rather than movement or change in position.