Unabridged means "not reduced in compass or scope by condensing, omitting, etc."; that is, it means "full-length" or "not cut." Abridged, conversely, implies reduction. Thus we speak of an unabridged dictionary when we refer to one that is large and definitive, including virtually everything that it could reasonably be expected to contain. An abridged dictionary is one which is considerably shorter but which still retains all, or nearly all, information considered essential. An expurgated book is one from which passages thought obscene or otherwise objectionable have been removed. Expurgated has a sense of purging, of cleansing. Abridged and unabridged imply "shortened" and "full-length," without any connotation of moral, social, or ethical values.
Dictionary of problem words and expressions. Harry Shaw. 1975.