What does the cryptic crossword clue "Gloomy sort of cleaner, about to retire (5)" mean?

The wordplay uses a reversal. MOP (synonym="cleaner") + RE (reversal="about") = MOPER The answer is MOPER.

Gloomy sort of cleaner, about to retire (5)

Guardian Cryptic #29393 | 7 Down | 2024-05-27 flower