The term 'ANTISEPTIC PIONEER' can be broken down into two crossword solutions: LISTER (6 letters) and IODOL (5 letters). Joseph Lister was a British surgeon who pioneered the use of antiseptic techniques in surgery. He was the first to use carbolic acid, now known as phenol, as an antiseptic. Iodol was an antiseptic solution developed by Lister which contained iodine and phenol. It was used to treat wounds and prevent infection.