Concept:An oxymoron is a figure of speech that combines two contradictory terms in one expression.Explanation:The phrase "faithful liar" brings together two opposing ideas: "faithful" suggests loyalty and honesty, while "liar" means one who tells falsehoods.This direct contradiction is a clear characteristic of an oxymoron.It is not a euphemism, antithesis, or epigram because it simply joins contradictory words to create a striking expression.Answer:D. oxymoron