IPA: /ˈɡɔːntnəs/
KK: /gɔntnɪs/
The state of being very thin and bony, often due to illness or lack of food.
His gauntness was a clear sign that he had been unwell for a long time.
Gauntness is formed from "gaunt" (from Middle English "gaunt", meaning thin or haggard) and the suffix "-ness" (meaning the state or quality of). The word "gauntness" refers to the state of being thin or haggard.
Think of someone who looks very thin or haggard — that's what 'gauntness' means, the quality of being gaunt.