D defs.my
Entry 1 sense Webster, 1913

Thionyl

· Thi·on·yl · IPA
01 n. The hypothetical radical SO, regarded as an essential constituent of certain sulphurous compounds; as, thionyl chloride.
  1. 1.
    The hypothetical radical SO, regarded as an essential constituent of certain sulphurous compounds; as, thionyl chloride.(Chem.)