The term 'MOST ARTFUL' can be solved by two six-letter words: SLIEST and SLYEST. SLIEST is an adjective meaning 'most skillful or ingenious, ' while SLYEST is an adjective meaning 'most cunning or crafty.' Both words refer to someone who is highly skilled in a particular area, but the difference between them is that SLIEST implies a more positive connotation, while SLYEST implies a more negative connotation.