What does the cryptic crossword clue "Don't purify murky depth (10)" mean?

The definition is "depth". The wordplay uses an anagram. anagram of DON'T + PURIFY = PROFUNDITY; definition: "depth" The answer is PROFUNDITY.

Don't purify murky depth (10)

Guardian Cryptic #27759 | 6 Down | 2019-03-04 flower