skittishness vs nervousness

skittishness and nervousness both are nouns.

Word	Noun	Adjective	Verb	Adverb
skittishness	Yes	No	No	No
nervousness	Yes	No	No	No

As nouns, nervousness is a hypernym of skittishness; that is, nervousness is a word with a broader meaning than skittishness:

skittishness (noun)	nervousness (noun)
characterized by nervousness and quickness to take fright	a sensitive or highly strung temperament
	the anxious feeling you have when you have the jitters
	an uneasy psychological state