Source : Webster's Revised Unabridged Dictionary (1913)

Nitrosyl \Ni*tro"syl\, n. [Nitroso- + -yl.] (Chem.)
   the radical {NO}, called also the {nitroso group}. The term
   is sometimes loosely used to designate certain nitro
   compounds; as, nitrosyl sulphuric acid. Used also
   adjectively.