Being "under quarantine" refers to the state of being confined or isolated to avoid the spread of infectious disease. When looking for synonyms for the phrase, one can use words like "quarantined," "isolated," "segregated," "contained," or "restricted," all of which point to the idea of being separated from others. Additionally, "locked down," "shut-in," and "sealed off" are also suitable alternatives. Despite their differences, all of these words highlight the importance of taking precautions and ensuring the safety of oneself and others during times of disease or contagion.