quack [L16th] ‘If it looks like a duck, walks like a duck, and quacks like a duck, then it just may be a duck.’ was the comment made by the US union leader Walter Reuther about the alleged communists investigated by Senator Joseph McCarthy in the early 1950s. The quack of a duck, recorded from the late 16th century (although the form queck is Middle English), is just an imitation of the bird’s characteristic sound. The kind of quack who dishonestly claims to have medical skills was originally a quacksalver, a 17th-century word from Dutch quacken ‘to talk foolishly’ and salf the same word as ‘salve’ [OE] from a Germanic base meaning ‘clarified butter’.