General uncleanliness:
* Filthy: More extreme than dirty, emphasizing a heavy layer of dirt.
* Soiled: Usually refers to something stained or marked with dirt.
* Grimy: Implies something sticky and covered in dirt, often greasy.
* Unclean: Formal and emphasizes a lack of hygiene.
* Unsanitary: Focuses on the potential for disease or infection.
* Fouled: Often refers to something contaminated, usually with waste.
More specific to the type of dirt:
* Dusty: Covered in dust.
* Muddy: Covered in mud.
* Grease-stained: Covered in grease.
* Smoky: Covered in soot or smoke.
* Rusty: Covered in rust.
Figurative meanings:
* Dishonorable: Used metaphorically to describe something morally corrupt.
* Sordid: Implies something morally repulsive and disgusting.
* Tainted: Implies something has been corrupted or damaged.
Informal slang:
* Grungy: Refers to something messy and unkempt.
* Scruffy: Often describes someone who is messy and untidy.
* Skeezy: Used for something that is dirty and undesirable.
It's important to consider the context and the specific nuance you want to convey when choosing a synonym for "dirty."