scab [ME] This comes from Old Norse, going back to a Germanic root meaning ‘itch’. The sense ‘contemptible person’ dating from the late 16th century was probably influenced by Middle Dutch schabbe ‘slut’. It was used to refer to a a strike breaker from the mid 18th century, originally in the USA. Shabby [M17th] comes from a dialect variant of the source of scab. Dr Johnson wrote that shabby was: ‘A word that has crept into conversation and low writing, but ought not to be admitted into the language’.