"Keep aside" is a commonly used phrase that means to reserve or set something apart for later use. However, there are several synonyms that can be used in its place, depending on the context. One alternative is "set aside," which retains the same meaning but offers a slightly more formal tone. Another option is "put aside," which emphasizes the action of physically moving something away from its original location. Other synonyms include "reserve," "hold back," "stash," "save," and "preserve." Each of these options offers a unique nuance that can enhance the meaning of a sentence by providing greater specificity or variety in word choice.