The etymologists are not too clear about it either. William Smith, the great Latinist thought that obscaenus might have come from caenum, which meant dirt, with the ob- as a sort of intensifier, but Oxford says "of doubtful etymology", perhaps worried about that intrusive "s". In English, people often used to say something was obscene when all they meant was that it was grubby or unwashed: one might speak of an obscene dog, or an obscene beggar, whose only sin was that he had no access to a pump. This supports Sir William Smith's theory. Even as late as the 1920s we have Arnold Bennett writing about a run-down part of town where "the areas [he meant the basement areas of the houses], except one or two, were obscene".
We have forgotten that side of it now. The filth we talk about is all metaphorical filth the sort of thing which, in the familiar words of the Obscene Publications Acts, "tends to deprave or corrupt". In the 1950s, if you asked anyone what the word meant, they would tend to lie back and think of Lady Chatterley.
Since then a curious thing has happened. Obscene, having concentrated its meaning, has expanded it again. I'm not sure when this began to happen, perhaps in the mid 1960s. Anything with which the speaker disagrees strongly enough can now be described as obscene - the income of a fat-cat, the prodigality of a town hall, the destruction of wildlife site, a prisoner's early release. The legal meaning, with the unpleasant image evoked by it, has given new life to the metaphor.Reuse content