Coinstantaneous is a less commonly used word to describe two or more things that happen simultaneously or at the same time. Some synonyms for coinstantaneous include simultaneous, synchronous, concurrent, coexistent, and parallel. These words can be used interchangeably with coinstantaneous in sentences such as "The two events were simultaneous" or "The actions of the two people were synchronous." Other synonyms for this word include contemporaneous, coincident, and concomitant. It is important to note that while these words have similar meanings, they may have slightly different nuances or connotations, so it is important to choose the right word based on the context in which it is used.