Holding ransom refers to the act of keeping someone or something captive to obtain ransom in return. There are various synonymous phrases that can be used in place of holding ransom. One such phrase is "taking hostage," which means to capture someone and use them as leverage to receive something in return. Another similar phrase is "keeping someone at bay," which describes the action of keeping someone restrained or under control. A more formal term is "extortion," which implies the use of threats or force to obtain money or other advantages. Finally, "blackmail" can be used to refer to the act of holding someone ransom for gain. Ultimately, these synonyms help express the same concept of taking something hostage to obtain a ransom.