Character Hui

秽 means filthy, overgrown, or morally foul.

The earliest dictionary trail is for the related form 薉, glossed as overgrown or weed-choked. Its practical starting point was land left clogged with weeds, not an abstract symbol for badness.

The recorded range then widens to dirt and impurity, disorder, ugly or evil conduct, and sexual obscenity. A bare gloss such as dirty is therefore too narrow; the compound or sentence supplies the target.

Why does 秽 sound different in different compounds?

The compound decides whether it is dirt or condemnation.

污秽 describes filth or impurity; 淫秽 marks obscenity; 秽语 marks foul or indecent language. The character can therefore move from a physical description to a judgment about conduct or speech.

The form history is part of the trap: 《说文解字》 records 薉, while later lexicographic tradition records 穢, and simplified Chinese writes 秽. 穢 is the corresponding traditional form, not a separate meaning. Match the script of the surrounding text.