Preinstruct refers to the act of providing instructions in advance. However, there are several synonyms that can be used in place of this word. One synonym is "preteach," which means to teach something beforehand. Another option is "forewarn," which means to give a warning or advice before an event or situation occurs. "Preeducate" is another synonym that can be used to mean the same thing as preinstruct. Other synonyms for preinstruct include "prime," "instruct in advance," "prepare," and "familiarize." These words can be used interchangeably, depending on the context of the conversation, and can help to vary the language and make writing more interesting.