As nouns the difference between steadfastness and unflinchingness
is that steadfastness is loyalty in the face of trouble and difficulty while unflinchingness is the state or condition of being unflinching; steadfastness, resoluteness.
steadfastness
English
Noun
Loyalty in the face of trouble and difficulty.
Steadfast resolution.
unflinchingness
English
Noun
(-)
The state or condition of being unflinching; steadfastness, resoluteness.