"filthiest" in the adjective sense
1. filthy, foul, nasty
disgustingly dirty filled or smeared with offensive matter
"as filthy as a pigsty"
"a foul pond"
"a nasty pigsty of a room"
2. dirty, filthy, lousy
vile despicable
"a dirty (or lousy) trick"
"a filthy traitor"
3. cruddy, filthy, foul, nasty, smutty
characterized by obscenity
"had a filthy mouth"
"foul language"
"smutty jokes"
Source: WordNet® (An amazing lexical database of English)
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