Baretti: A dictionary of the English and Italian languages
Sottigliézza, s. f.
1. subtilty; 2. sharpness, thinness.— d'aria, sharpness of air. — di mente,clearness of understanding; 3. subtlety, craft, subtle trick; 4. want, scarcity, need, penury;5. delicacy of wit. La — dell'arte, the beauty of the art; 6. one of the gifts enjoyed by the blessed in heaven.
Florio: a worlde of wordes, or most copious, dictionarie in Italian and English
sottigliezza: subtility, subtilnesse, finenesse, sinalnesse, littlenesse, sharpe- nesse, slendernesse. Also slinesse or quicknesse of wit or aire.