the.com/sternness

means A severe, unsmiling strictness in manner or expression, often used to enforce discipline without raising a voice.

from From 'stern,' an Old English word (stierne/styrne) related to Germanic roots carrying the sense of 'hard, severe, resolute.' It's a cousin of words meaning 'to stare' or 'fix rigidly' in some older Germanic languages — the harsh, unyielding look giving the word its backbone. The '-ness' is just the standard Old English suffix bolted on to turn the quality into a noun — nothing poetic there, just grammar doing its job.