variant of sulf-.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
containing sulphursulphate; sulphonic acid
The ``ph'' spelling of sulphur and related words is used in British English. In the US the spelling is sulfur . However, the recommended spelling in chemistry is sulfur and this is found in technical writing. Also the sulf- spelling is used in the names of generic drugs
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012