A fiber finish composition, a process which includes treating polyester yarn therewith and polyester yarn so treated are all disclosed. The fiber finish composition comprises a triglycidyl ether of glycerol; a low viscosity diglycidyl ether having the structural formula ##STR1## wherein R is alkylene or arylene; ethoxylated castor oil; an epoxy silane having the structural formula ##STR2## wherein n=2 to 5; and a solvent. The process comprises the steps of (1) heating the yarn to a temperature of about 150.degree. C. to 230.degree. C. and (2) treating the yarn with the fiber finish composition, preferably utilized as an aqueous overfinish. The yarn is preferably used in tire cords for the construction of pneumatic passenger tires and results in excellent adhesion of tire cord to rubber.