The word "invisibles" is a term used to describe things that are not visible to the naked eye or imperceptible to the senses. There are many synonyms that can be used in place of "invisibles" to convey the same meaning. Some such words include "hidden," "obscure," "unseen," "unnoticed," "mysterious," "cryptic," "enigmatic," "unfathomable" and "imperceptible." These words not only describe things that are invisible, but also give a sense of mystery and intrigue. By using these synonyms, one can add depth and nuance to their writing, making it more interesting and engaging.