an abundant tasteless odorless multivalent nonmetallic element; best known in yellow crystals; occurs in many sulphide and sulphate minerals and even in native form (especially in volcanic regions)
"Geologists collected samples of sulfur from the volcanic vents, noting its characteristic yellow crystalline appearance."
A chemical element (symbol S) with an atomic number of 16.
"Sulfur is a yellow chemical element with the symbol S and an atomic number of 16 that gives volcanic regions their distinct smell."
In plain English: Sulfur is a yellow element found naturally on Earth that gives rotten eggs their smell and helps make gunpowder burn brightly.
"The rotten egg smell came from sulfur released by the volcano."
Usage: Use the spelling "sulfur" in American English and "sulphur" in British English when referring to the element or its compounds. Avoid using this term for the bright yellow substance found in volcanoes unless specifically discussing its chemical properties.
To treat with sulfur, or a sulfur compound, especially to preserve or to counter agricultural pests.
"Farmers often sulfur their apple trees to protect them from harmful insects and fungal diseases."
In plain English: Sulfur is not used as a verb, so it cannot be defined that way because it only exists as an element or mineral name.
"The ancient alchemist believed he could sulfur lead by heating its ore with salt and nitre."
Of a yellowish green colour, like that of sulfur.
"The pale, yellowish-green moss growing on the old wall reminded me vividly of sulfur."
In plain English: There is no adjective form of sulfur because it is always used as a noun to name the yellow element found on the periodic table.
"The sulfur smell was strong after we opened the eggs."
The word comes from the Latin sulfur, which entered English via Anglo-Norman and Middle English. Its ultimate origin is unknown, but it replaced the older Old English term swefl.