Im pan də rə bəl
adjective
unable to be evaluated or calculated accurately.
…There is beneath my birth, life, death, a substratum of supernatural causes, imponderable, invisible, unknowable by any physical science whatsoever. (Charles Kingsley, The Ancien Regime)
noun
something that cannot be evaluated or calculated with exactness.
The divinity-student came and read over her shoulder, very curious, apparently, but his eyes wandered, I thought. Fancying that her breathing was somewhat hurried and high, or thoracic, as my friend, the Professor, calls it, I watched her a little more closely. It is none of my business. After all, it is the imponderables that move the world,–heat, electricity, love. (Oliver Wendell Holmes, Autocrat of the Breakfast Table)