For physical cleanliness:
* Filthy: (stronger than "dirty")
* Soiled: (implies something has been stained or marked)
* Grimy: (implies a sticky or oily dirtiness)
* Unclean: (more formal than "dirty")
* Polluted: (implies contamination)
* Dusty: (specific to dust)
* Muddy: (specific to mud)
* Stained: (implies a mark or discoloration)
For moral or ethical implications:
* Corrupt: (implies dishonest or illegal behavior)
* Dishonest: (implies a lack of truthfulness)
* Sordid: (implies something morally wrong or shameful)
* Immoral: (implies a violation of ethical principles)
* Unlawful: (implies something illegal)
* Unclean: (can also have a moral connotation)
* Scandalous: (implies something shocking or disgraceful)
More informal synonyms:
* Gross: (implies something disgusting or unpleasant)
* Yucky: (informal and childish)
* Nasty: (implies something unpleasant or harmful)
* Grungy: (implies a neglected and messy appearance)
To choose the best synonym, consider the specific meaning you want to convey and the context in which you are using it.