This word is acceptable for play in the UK dictionary that is being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

Incapable of being measured or sounded with a plummet or lead-line; unfathomable.

"With his unbending, utilitarian, matter – of – fact face, he hardened her again; and the moment shot away into the plumbless depths of the past, to mingle with all the lost opportunities that are drowned there."