These words refer to things impure, defiled, adulterated or layered with foreign matter. Dirty can refer to a lack of cleanliness that comes about through normal use: a pile of dirty clothes to be sent to the laundry. It can also suggest an unusual or more extreme cause: a dust storm that had left everything in the house dirty . The word has more force in reference to impure morals: dirty stories; a dirty old man. Soiled concentrates mostly on things made dirty through normal use: a soiled apron; hands soiled from working in the garden. The word can suggest a layering over something with dirt or soil. In the moral context the word is even more forceful than dirty: a soiled reputation.

On the literal level, neither of the previous words need suggest disapproval for what may be a natural process. Filthy , however, suggests something extremely dirty and, possibly, disgusting or noxious: an unkempt tramp whose clothing was filthy . Morally the word serves as an intensification of dirty but the specific context is even more likely to be sexual in nature: lewd and filthy acts; pornography that included filthy pictures. Squalid adds to the implications of filthy a sense of disarray, disorder and distasteful rankness: squalid slums. In reference to morals the word suggests habits and patterns considerably outside the norm: hippies who live squalid fly-by-night lives.

Foul now is largely restricted to what is morally reprehensible; its disapproval is vague, attaching to anything the user may deplore: a foul traitor. Language that includes so-called dirty words is often called foul . Unclean can be used neutrally for anything soiled but oddly enough, it is particularly suggestive of a moral or religious context: unclean in mind and spirit. Sordid , more than any of the other words here, fuses together references to both physical and moral uncleanliness: sordid crimes committed in a sordid environment.