A Dictionary of Music and Musicians/Arioso
ARIOSO. Literally 'airy.' Used substantively, it would seem to mean that kind of air which, partaking both of the character of air and recitative, requires rather to be said than sung. Mendelssohn's two pieces, 'But the Lord is mindful' and 'Woe unto them that forsake Him' are marked 'Arioso,' and are both of the character indicated.
[ J. H. ]