Synonyms for Slightness (same or very similar meaning)
WordNet sense 1 (the quality of being unimportant and petty or frivolous):
pettiness, puniness, trivialityWordNet sense 2 (smallness of stature):
delicacyWordNet sense 3 (the property of an attractively thin person):
slenderness, slimnessFrom the ODE community, based on WordNetadd/edit