'gauntness' is formed from the adjective 'gaunt' plus the noun-forming suffix '-ness'; 'gaunt' itself is recorded in Middle English as 'gaunt', of uncertain origin.

The adjective 'gaunt' appeared in Middle English (as 'gaunt') and passed into Modern English largely unchanged in form; the noun 'gauntness' developed by adding the suffix '-ness' to denote the state or quality.

Originally describing someone thin or emaciated, the sense has remained largely the same but has also extended metaphorically to describe bleakness or severity in appearance.