Meaning

noun relatively small dimension through an object as opposed to its length or width

noun the property of having little body fat

noun the property of being very narrow or thin

originFrom Middle English thynnesse, from Old English þynnes (“thinness, slightness of density, lack of density, tenuity, fluidity, poverty, feebleness of sight, weakness”), equivalent to thin + -ness.

Etymology from Wiktionary, CC BY-SA 3.0