The phrase "not worth a plug nickel" refers to something that is worthless or of little value. There are many synonyms for this phrase, including "not worth a penny," "not worth a dime," "not worth a cent," "worthless," "valueless," "useless," and "pointless." These words convey the same idea that the object or idea in question is of no importance and provides no real benefit. When we use such phrases, we typically communicate an opinion or critique regarding something's lack of value, often in the context of business, finance, or personal relationships. Overall, there are many ways to describe things that lack worth or value, each with its nuanced connotations.