The word "plumbless" is an adjective that means impossible to fathom or measure. There are many synonyms for plumbless that you can use to add variety to your writing. Some options include bottomless, immeasurable, infinite, unfathomable, unbounded, limitless, boundless, incomprehensible, endless, incalculable, inexhaustible, and measureless. Each of these words conveys a similar meaning to plumbless, and you can choose the one that fits best in the context of your writing. Whether you are writing a novel, a technical report, or a blog post, using synonyms will help you avoid using the same words over and over again.