When you want to talk about just one thing, there are plenty of synonyms to choose from. For instance, you could use the word "singular" to convey the idea of any one thing - as in, "I'm looking for a singular solution to our company's problems." Or, if you want to emphasize the idea of choice or selection, you might use "option" instead - such as, "Do you have any options for dinner tonight?" Other synonyms for any one thing might include "individual," "specific," "particular," "unique," "distinct," or "solitary." All of these words can help you express the idea of a single object or entity, without resorting to the more common phrase "any one thing".