The quality of being staunch — the steady, unshakeable loyalty itself, thought of as a thing a person has. You would use it in a sentence like "his staunchness surprised everyone", where you are naming the trait rather than describing an action. It is uncountable: staunchness, never "a staunchness" or "staunchnesses". Be aware that this is the least used member of its family by a wide margin. English speakers will understand it, but in real writing they far more often use the adjective (a staunch friend) or the adverb (staunchly loyal), or reach for a commoner noun — loyalty, steadfastness, devotion. If you want your English to sound natural, learn staunch and staunchly first and keep this one as a word you recognise rather than one you produce.

堅定、忠貞不移（性格特質）