There are various synonyms for the phrase "in reserve." This phrase is commonly used to indicate something that is being held back or saved for later use. Alternative words that have similar meanings include "on standby," "in storage," "reserved," "stockpiled," and "set aside." All of these phrases suggest that something is being kept in reserve for a future need or contingency. "On standby" is often used in reference to technology or equipment that is ready to be used at a moment's notice. "In storage" and "stockpiled" indicate that something is being kept in a physical location until it is needed, while "reserved" and "set aside" suggest that something has been designated for a particular purpose or person.