(filthier, filthiest)
1.
Something that is filthy is very dirty indeed.
He never washed, and always wore a filthy old jacket.
= grimy
ADJ
2.
If you describe something as filthy, you mean that you think it is morally very unpleasant and disgusting, sometimes in a sexual way.
The play was full of filthy foul language.
ADJ [disapproval]
3.