is that tan is Total Acid Number, the measure of a lubricant's or crude oil's acidity while CSC is criminal Sexual Conduct.
As a noun tan
is a yellowish-brown colour.
As an adjective tan
is of a yellowish-brown.
As a verb tan
is to change to a tan colour due to exposure to the sun.
As a numeral tan
is the second cardinal number two, formerly used in Celtic areas, especially Cumbria and parts of Yorkshire, for counting sheep, and stitches in knitting.See Wikipedia article on Yan Tan Tethera