What does the cryptic crossword clue "Good-for-nothing Dawn shortly about to bale out (8)" mean?

The wordplay uses an anagram. UNUS (synonym="UNUS") + ABLE (synonym="ABLE") = UNUSABLE The answer is UNUSABLE.

Good-for-nothing Dawn shortly about to bale out (8)

Guardian Cryptic #29491 | 14 Down | 2024-09-18 flower