The phrase "under threat" refers to a state of danger or risk of harm or loss. There are various synonyms that can be used to express the same meaning, such as "in jeopardy," "at risk," "in danger," "endangered," "vulnerable," "exposed," "in peril," "under attack," "under fire," "under siege," "menaced," "imperiled," and "under pressure." These synonyms highlight the level of insecurity or uncertainty that is associated with the threat. They are often used to describe situations where individuals, groups or entities are facing challenges or adversities that require immediate attention or action to prevent or minimize the potential harm or damage.